MySQL/MariaDB数据库的多表查询操作
作者：尹正杰
版权声明：原创作品，谢绝转载！否则将追究法律责任。
一.单表查询小试牛刀
[root@node105.yinzhengjie.org.cn ~]# cat yinzhengjie_innodb.sql -- MySQL dump 10.13 Distrib 5.5.33, for Linux (x86_64) -- -- Host: localhost Database: yinzhengjie -- ------------------------------------------------------ -- Server version 5.5.33-log /*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */; /*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */; /*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */; /*!40101 SET NAMES utf8 */; /*!40103 SET @OLD_TIME_ZONE=@@TIME_ZONE */; /*!40103 SET TIME_ZONE='+00:00' */; /*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */; /*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */; /*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */; /*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */; -- -- Current Database: `yinzhengjie` -- CREATE DATABASE /*!32312 IF NOT EXISTS*/ `yinzhengjie` /*!40100 DEFAULT CHARACTER SET utf8 */; USE `yinzhengjie`; -- -- Table structure for table `classes` -- DROP TABLE IF EXISTS `classes`; /*!40101 SET @saved_cs_client = @@character_set_client */; /*!40101 SET character_set_client = utf8 */; CREATE TABLE `classes` ( `ClassID` tinyint(3) unsigned NOT NULL AUTO_INCREMENT, `Class` varchar(100) DEFAULT NULL, `NumOfStu` smallint(5) unsigned DEFAULT NULL, PRIMARY KEY (`ClassID`) ) ENGINE=InnoDB AUTO_INCREMENT=9 DEFAULT CHARSET=utf8; /*!40101 SET character_set_client = @saved_cs_client */; -- -- Dumping data for table `classes` -- LOCK TABLES `classes` WRITE; /*!40000 ALTER TABLE `classes` DISABLE KEYS */; INSERT INTO `classes` VALUES (1,'Shaolin Pai',10),(2,'Emei Pai',7),(3,'QingCheng Pai',11),(4,'Wudang Pai',12),(5,'Riyue Shenjiao',31),(6,'Liansha n Pai',27),(7,'Ming Jiao',27),(8,'Xiaoyao Pai',15);/*!40000 ALTER TABLE `classes` ENABLE KEYS */; UNLOCK TABLES; -- -- Table structure for table `coc` -- DROP TABLE IF EXISTS `coc`; /*!40101 SET @saved_cs_client = @@character_set_client */; /*!40101 SET character_set_client = utf8 */; CREATE TABLE `coc` ( `ID` int(10) unsigned NOT NULL AUTO_INCREMENT, `ClassID` tinyint(3) unsigned NOT NULL, `CourseID` smallint(5) unsigned DEFAULT NULL, PRIMARY KEY (`ID`) ) ENGINE=InnoDB AUTO_INCREMENT=15 DEFAULT CHARSET=utf8; /*!40101 SET character_set_client = @saved_cs_client */; -- -- Dumping data for table `coc` -- LOCK TABLES `coc` WRITE; /*!40000 ALTER TABLE `coc` DISABLE KEYS */; INSERT INTO `coc` VALUES (1,1,2),(2,1,5),(3,2,2),(4,2,6),(5,3,1),(6,3,7),(7,4,5),(8,4,2),(9,5,1),(10,5,9),(11,6,3),(12,6,4),(13,7,4),(14,7,3); /*!40000 ALTER TABLE `coc` ENABLE KEYS */; UNLOCK TABLES; -- -- Table structure for table `courses` -- DROP TABLE IF EXISTS `courses`; /*!40101 SET @saved_cs_client = @@character_set_client */; /*!40101 SET character_set_client = utf8 */; CREATE TABLE `courses` ( `CourseID` smallint(5) unsigned NOT NULL AUTO_INCREMENT, `Course` varchar(100) NOT NULL, PRIMARY KEY (`CourseID`) ) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8; /*!40101 SET character_set_client = @saved_cs_client */; -- -- Dumping data for table `courses` -- LOCK TABLES `courses` WRITE; /*!40000 ALTER TABLE `courses` DISABLE KEYS */; INSERT INTO `courses` VALUES (1,'Hamo Gong'),(2,'Kuihua Baodian'),(3,'Jinshe Jianfa'),(4,'Taiji Quan'),(5,'Daiyu Zanghua'),(6,'Weituo Zhang'),(7, 'Dagou Bangfa');/*!40000 ALTER TABLE `courses` ENABLE KEYS */; UNLOCK TABLES; -- -- Table structure for table `scores` -- DROP TABLE IF EXISTS `scores`; /*!40101 SET @saved_cs_client = @@character_set_client */; /*!40101 SET character_set_client = utf8 */; CREATE TABLE `scores` ( `ID` int(10) unsigned NOT NULL AUTO_INCREMENT, `StuID` int(10) unsigned NOT NULL, `CourseID` smallint(5) unsigned NOT NULL, `Score` tinyint(3) unsigned DEFAULT NULL, PRIMARY KEY (`ID`) ) ENGINE=InnoDB AUTO_INCREMENT=16 DEFAULT CHARSET=utf8; /*!40101 SET character_set_client = @saved_cs_client */; -- -- Dumping data for table `scores` -- LOCK TABLES `scores` WRITE; /*!40000 ALTER TABLE `scores` DISABLE KEYS */; INSERT INTO `scores` VALUES (1,1,2,77),(2,1,6,93),(3,2,2,47),(4,2,5,97),(5,3,2,88),(6,3,6,75),(7,4,5,71),(8,4,2,89),(9,5,1,39),(10,5,7,63),(11,6, 1,96),(12,7,1,86),(13,7,7,83),(14,8,4,57),(15,8,3,93);/*!40000 ALTER TABLE `scores` ENABLE KEYS */; UNLOCK TABLES; -- -- Table structure for table `students` -- DROP TABLE IF EXISTS `students`; /*!40101 SET @saved_cs_client = @@character_set_client */; /*!40101 SET character_set_client = utf8 */; CREATE TABLE `students` ( `StuID` int(10) unsigned NOT NULL AUTO_INCREMENT, `Name` varchar(50) NOT NULL, `Age` tinyint(3) unsigned NOT NULL, `Gender` enum('F','M') NOT NULL, `ClassID` tinyint(3) unsigned DEFAULT NULL, `TeacherID` int(10) unsigned DEFAULT NULL, PRIMARY KEY (`StuID`) ) ENGINE=InnoDB AUTO_INCREMENT=26 DEFAULT CHARSET=utf8; /*!40101 SET character_set_client = @saved_cs_client */; -- -- Dumping data for table `students` -- LOCK TABLES `students` WRITE; /*!40000 ALTER TABLE `students` DISABLE KEYS */; INSERT INTO `students` VALUES (1,'Shi Zhongyu',22,'M',2,3),(2,'Shi Potian',22,'M',1,7),(3,'Xie Yanke',53,'M',2,16),(4,'Ding Dian',32,'M',4,4),(5, 'Yu Yutong',26,'M',3,1),(6,'Shi Qing',46,'M',5,NULL),(7,'Xi Ren',19,'F',3,NULL),(8,'Lin Daiyu',17,'F',7,NULL),(9,'Ren Yingying',20,'F',6,NULL),(10,'Yue Lingshan',19,'F',3,NULL),(11,'Yuan Chengzhi',23,'M',6,NULL),(12,'Wen Qingqing',19,'F',1,NULL),(13,'Tian Boguang',33,'M',2,NULL),(14,'Lu Wushuang',17,'F',3,NULL),(15,'Duan Yu',19,'M',4,NULL),(16,'Xu Zhu',21,'M',1,NULL),(17,'Lin Chong',25,'M',4,NULL),(18,'Hua Rong',23,'M',7,NULL),(19,'Xue Baochai',18,'F',6,NULL),(20,'Diao Chan',19,'F',7,NULL),(21,'Huang Yueying',22,'F',6,NULL),(22,'Xiao Qiao',20,'F',1,NULL),(23,'Ma Chao',23,'M',4,NULL),(24,'Xu Xian',27,'M',NULL,NULL),(25,'Sun Dasheng',100,'M',NULL,NULL);/*!40000 ALTER TABLE `students` ENABLE KEYS */; UNLOCK TABLES; -- -- Table structure for table `teachers` -- DROP TABLE IF EXISTS `teachers`; /*!40101 SET @saved_cs_client = @@character_set_client */; /*!40101 SET character_set_client = utf8 */; CREATE TABLE `teachers` ( `TID` smallint(5) unsigned NOT NULL AUTO_INCREMENT, `Name` varchar(100) NOT NULL, `Age` tinyint(3) unsigned NOT NULL, `Gender` enum('F','M') DEFAULT NULL, PRIMARY KEY (`TID`) ) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8; /*!40101 SET character_set_client = @saved_cs_client */; -- -- Dumping data for table `teachers` -- LOCK TABLES `teachers` WRITE; /*!40000 ALTER TABLE `teachers` DISABLE KEYS */; INSERT INTO `teachers` VALUES (1,'Song Jiang',45,'M'),(2,'Zhang Sanfeng',94,'M'),(3,'Miejue Shitai',77,'F'),(4,'Lin Chaoying',93,'F'); /*!40000 ALTER TABLE `teachers` ENABLE KEYS */; UNLOCK TABLES; -- -- Table structure for table `toc` -- DROP TABLE IF EXISTS `toc`; /*!40101 SET @saved_cs_client = @@character_set_client */; /*!40101 SET character_set_client = utf8 */; CREATE TABLE `toc` ( `ID` int(10) unsigned NOT NULL AUTO_INCREMENT, `CourseID` smallint(5) unsigned DEFAULT NULL, `TID` smallint(5) unsigned DEFAULT NULL, PRIMARY KEY (`ID`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8; /*!40101 SET character_set_client = @saved_cs_client */; -- -- Dumping data for table `toc` -- LOCK TABLES `toc` WRITE; /*!40000 ALTER TABLE `toc` DISABLE KEYS */; /*!40000 ALTER TABLE `toc` ENABLE KEYS */; UNLOCK TABLES; /*!40103 SET TIME_ZONE=@OLD_TIME_ZONE */; /*!40101 SET SQL_MODE=@OLD_SQL_MODE */; /*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */; /*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */; /*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */; /*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */; /*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */; /*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */; -- Dump completed on 2013-09-03 2:51:27 [root@node105.yinzhengjie.org.cn ~]#
导入yinzhengjie_innodb.sql生成数据库及相应的测试表数据信息，然后完成下面问题。
[root@node105.yinzhengjie.org.cn ~]# mysql -uroot -pyinzhengjie -S /mysql/3306/socket/mysql.sock Welcome to the MariaDB monitor. Commands end with ; or g. Your MariaDB connection id is 17 Server version: 10.2.19-MariaDB MariaDB Server Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others. Type 'help;' or 'h' for help. Type 'c' to clear the current input statement. MariaDB [(none)]> MariaDB [(none)]> show databases; +--------------------+ | Database | +--------------------+ | information_schema | | mysql | | performance_schema | +--------------------+ rows in set (0.00 sec) MariaDB [(none)]> MariaDB [(none)]> SOURCE yinzhengjie_innodb.sql Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 1 row affected (0.00 sec) Database changed Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 8 rows affected (0.01 sec) Records: 8 Duplicates: 0 Warnings: 0 Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 14 rows affected (0.00 sec) Records: 14 Duplicates: 0 Warnings: 0 Query OK, 0 rows affected (0.01 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 7 rows affected (0.00 sec) Records: 7 Duplicates: 0 Warnings: 0 Query OK, 0 rows affected (0.01 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 15 rows affected (0.00 sec) Records: 15 Duplicates: 0 Warnings: 0 Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.01 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 25 rows affected (0.00 sec) Records: 25 Duplicates: 0 Warnings: 0 Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.01 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 4 rows affected (0.00 sec) Records: 4 Duplicates: 0 Warnings: 0 Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SHOW DATABASES; +--------------------+ | Database | +--------------------+ | information_schema | | mysql | | performance_schema | | yinzhengjie | +--------------------+ 4 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SHOW TABLES; +-----------------------+ | Tables_in_yinzhengjie | +-----------------------+ | classes | | coc | | courses | | scores | | students | | teachers | | toc | +-----------------------+ 7 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]>
1>.在students表中，查询年龄大于25岁，且为男性的同学的名字和年龄
MariaDB [yinzhengjie]> SELECT * FROM students; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+ 25 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT Name AS 姓名, Age AS 年龄 FROM students WHERE Age > 25 AND Gender = 'M'; +--------------+--------+ | 姓名 | 年龄 | +--------------+--------+ | Xie Yanke | 53 | | Ding Dian | 32 | | Yu Yutong | 26 | | Shi Qing | 46 | | Tian Boguang | 33 | | Xu Xian | 27 | | Sun Dasheng | 100 | +--------------+--------+ 7 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]>
2>.以ClassID为分组依据，显示每组的平均年龄
MariaDB [yinzhengjie]> SELECT * FROM students; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+ 25 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT ClassID,AVG(Age) FROM students GROUP BY ClassID; #查询的结果NULL那一行始终在最上面 +---------+----------+ | ClassID | AVG(Age) | +---------+----------+ | NULL | 63.5000 | | 1 | 20.5000 | | 2 | 36.0000 | | 3 | 20.2500 | | 4 | 24.7500 | | 5 | 46.0000 | | 6 | 20.7500 | | 7 | 19.6667 | +---------+----------+ 8 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT ClassID,AVG(Age) FROM students GROUP BY -ClassID DESC; #可以将NULL的结果放在最后一行输出 +---------+----------+ | ClassID | AVG(Age) | +---------+----------+ | 1 | 20.5000 | | 2 | 36.0000 | | 3 | 20.2500 | | 4 | 24.7500 | | 5 | 46.0000 | | 6 | 20.7500 | | 7 | 19.6667 | | NULL | 63.5000 | +---------+----------+ 8 rows in set (0.00 sec) MariaDB [yinzhengjie]>
3>.显示第2题中平均年龄大于30的分组及平均年龄
MariaDB [yinzhengjie]> SELECT * FROM students; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+ 25 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT ClassID,AVG(Age) FROM students GROUP BY -ClassID DESC; +---------+----------+ | ClassID | AVG(Age) | +---------+----------+ | 1 | 20.5000 | | 2 | 36.0000 | | 3 | 20.2500 | | 4 | 24.7500 | | 5 | 46.0000 | | 6 | 20.7500 | | 7 | 19.6667 | | NULL | 63.5000 | +---------+----------+ 8 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT ClassID,AVG(Age) AS age FROM students GROUP BY -ClassID DESC HAVING age >30; +---------+---------+ | ClassID | age | +---------+---------+ | 2 | 36.0000 | | 5 | 46.0000 | | NULL | 63.5000 | +---------+---------+ 3 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]>
4>.显示以L开头的名字的同学的信息
MariaDB [yinzhengjie]> SELECT * FROM students; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+ 25 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM students WHERE Name RLIKE '^L'; +-------+-------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+-------------+-----+--------+---------+-----------+ | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | +-------+-------------+-----+--------+---------+-----------+ 3 rows in set (0.00 sec) MariaDB [yinzhengjie]>
5>.显示TeacherID非空的同学的相关信息
MariaDB [yinzhengjie]> SELECT * FROM students; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+ 25 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM students WHERE TeacherID IS NOT NULL; +-------+-------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+-------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | +-------+-------------+-----+--------+---------+-----------+ 5 rows in set (0.00 sec) MariaDB [yinzhengjie]>
6>.以年龄排序后，显示年龄最大的前10位同学的信息
MariaDB [yinzhengjie]> SELECT * FROM students; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+ 25 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM students ORDER BY Age DESC LIMIT 10; +-------+--------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+--------------+-----+--------+---------+-----------+ | 25 | Sun Dasheng | 100 | M | NULL | NULL | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 4 | Ding Dian | 32 | M | 4 | 4 | | 24 | Xu Xian | 27 | M | NULL | NULL | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 17 | Lin Chong | 25 | M | 4 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | +-------+--------------+-----+--------+---------+-----------+ 10 rows in set (0.00 sec) MariaDB [yinzhengjie]>
7>.查询年龄大于等于20岁，小于等于25岁的同学的信息
MariaDB [yinzhengjie]> SELECT * FROM students; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+ 25 rows in set (0.00 sec) MariaDB [yinzhengjie]> SELECT * FROM students WHERE Age BETWEEN 20 AND 25; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | +-------+---------------+-----+--------+---------+-----------+ 10 rows in set (0.00 sec) MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> SELECT * FROM students; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+ 25 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM students WHERE Age >= 20 AND AGE <= 25; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | +-------+---------------+-----+--------+---------+-----------+ 10 rows in set (0.00 sec) MariaDB [yinzhengjie]>
二.多表查询(基于上面导入的"yinzhengjie_innodb.sql"数据进行演示)
博主推荐阅读: https://www.runoob.com/sql/sql-join.html
1>.将两张表中个别字段联合显示(纵向合并)
联合查询：UNION 拥有自动去重的功能 两张表中字段数量得相同 示例: SELECT Name,Age FROM students UNION SELECT Name,Age FROM teachers;
MariaDB [yinzhengjie]> SHOW TABLES; +-----------------------+ | Tables_in_yinzhengjie | +-----------------------+ | classes | | coc | | courses | | scores | | students | | teachers | | toc | +-----------------------+ 7 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM teachers; +-----+---------------+-----+--------+ | TID | Name | Age | Gender | +-----+---------------+-----+--------+ | 1 | Song Jiang | 45 | M | | 2 | Zhang Sanfeng | 94 | M | | 3 | Miejue Shitai | 77 | F | | 4 | Lin Chaoying | 93 | F | +-----+---------------+-----+--------+ 4 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM students; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+ 25 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT StuID AS id ,Name AS 姓名 FROM students UNION SELECT TID,Name FROM teachers; +----+---------------+ | id | 姓名 | +----+---------------+ | 1 | Shi Zhongyu | | 2 | Shi Potian | | 3 | Xie Yanke | | 4 | Ding Dian | | 5 | Yu Yutong | | 6 | Shi Qing | | 7 | Xi Ren | | 8 | Lin Daiyu | | 9 | Ren Yingying | | 10 | Yue Lingshan | | 11 | Yuan Chengzhi | | 12 | Wen Qingqing | | 13 | Tian Boguang | | 14 | Lu Wushuang | | 15 | Duan Yu | | 16 | Xu Zhu | | 17 | Lin Chong | | 18 | Hua Rong | | 19 | Xue Baochai | | 20 | Diao Chan | | 21 | Huang Yueying | | 22 | Xiao Qiao | | 23 | Ma Chao | | 24 | Xu Xian | | 25 | Sun Dasheng | | 1 | Song Jiang | | 2 | Zhang Sanfeng | | 3 | Miejue Shitai | | 4 | Lin Chaoying | +----+---------------+ 29 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]>
2>.笛卡尔乘积查询(又称交叉连接，横向合并，生成环境应该避免这种查询)
MariaDB [yinzhengjie]> SELECT * FROM students; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+ 25 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM teachers; +-----+---------------+-----+--------+ | TID | Name | Age | Gender | +-----+---------------+-----+--------+ | 1 | Song Jiang | 45 | M | | 2 | Zhang Sanfeng | 94 | M | | 3 | Miejue Shitai | 77 | F | | 4 | Lin Chaoying | 93 | F | +-----+---------------+-----+--------+ 4 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM students CROSS JOIN teachers; #笛卡尔积查询，生产环境应该避免这样的查询。 +-------+---------------+-----+--------+---------+-----------+-----+---------------+-----+--------+ | StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name | Age | Gender | +-------+---------------+-----+--------+---------+-----------+-----+---------------+-----+--------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 1 | Song Jiang | 45 | M | | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 2 | Zhang Sanfeng | 94 | M | | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 3 | Miejue Shitai | 77 | F | | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 4 | Lin Chaoying | 93 | F | | 2 | Shi Potian | 22 | M | 1 | 7 | 1 | Song Jiang | 45 | M | | 2 | Shi Potian | 22 | M | 1 | 7 | 2 | Zhang Sanfeng | 94 | M | | 2 | Shi Potian | 22 | M | 1 | 7 | 3 | Miejue Shitai | 77 | F | | 2 | Shi Potian | 22 | M | 1 | 7 | 4 | Lin Chaoying | 93 | F | | 3 | Xie Yanke | 53 | M | 2 | 16 | 1 | Song Jiang | 45 | M | | 3 | Xie Yanke | 53 | M | 2 | 16 | 2 | Zhang Sanfeng | 94 | M | | 3 | Xie Yanke | 53 | M | 2 | 16 | 3 | Miejue Shitai | 77 | F | | 3 | Xie Yanke | 53 | M | 2 | 16 | 4 | Lin Chaoying | 93 | F | | 4 | Ding Dian | 32 | M | 4 | 4 | 1 | Song Jiang | 45 | M | | 4 | Ding Dian | 32 | M | 4 | 4 | 2 | Zhang Sanfeng | 94 | M | | 4 | Ding Dian | 32 | M | 4 | 4 | 3 | Miejue Shitai | 77 | F | | 4 | Ding Dian | 32 | M | 4 | 4 | 4 | Lin Chaoying | 93 | F | | 5 | Yu Yutong | 26 | M | 3 | 1 | 1 | Song Jiang | 45 | M | | 5 | Yu Yutong | 26 | M | 3 | 1 | 2 | Zhang Sanfeng | 94 | M | | 5 | Yu Yutong | 26 | M | 3 | 1 | 3 | Miejue Shitai | 77 | F | | 5 | Yu Yutong | 26 | M | 3 | 1 | 4 | Lin Chaoying | 93 | F | | 6 | Shi Qing | 46 | M | 5 | NULL | 1 | Song Jiang | 45 | M | | 6 | Shi Qing | 46 | M | 5 | NULL | 2 | Zhang Sanfeng | 94 | M | | 6 | Shi Qing | 46 | M | 5 | NULL | 3 | Miejue Shitai | 77 | F | | 6 | Shi Qing | 46 | M | 5 | NULL | 4 | Lin Chaoying | 93 | F | | 7 | Xi Ren | 19 | F | 3 | NULL | 1 | Song Jiang | 45 | M | | 7 | Xi Ren | 19 | F | 3 | NULL | 2 | Zhang Sanfeng | 94 | M | | 7 | Xi Ren | 19 | F | 3 | NULL | 3 | Miejue Shitai | 77 | F | | 7 | Xi Ren | 19 | F | 3 | NULL | 4 | Lin Chaoying | 93 | F | | 8 | Lin Daiyu | 17 | F | 7 | NULL | 1 | Song Jiang | 45 | M | | 8 | Lin Daiyu | 17 | F | 7 | NULL | 2 | Zhang Sanfeng | 94 | M | | 8 | Lin Daiyu | 17 | F | 7 | NULL | 3 | Miejue Shitai | 77 | F | | 8 | Lin Daiyu | 17 | F | 7 | NULL | 4 | Lin Chaoying | 93 | F | | 9 | Ren Yingying | 20 | F | 6 | NULL | 1 | Song Jiang | 45 | M | | 9 | Ren Yingying | 20 | F | 6 | NULL | 2 | Zhang Sanfeng | 94 | M | | 9 | Ren Yingying | 20 | F | 6 | NULL | 3 | Miejue Shitai | 77 | F | | 9 | Ren Yingying | 20 | F | 6 | NULL | 4 | Lin Chaoying | 93 | F | | 10 | Yue Lingshan | 19 | F | 3 | NULL | 1 | Song Jiang | 45 | M | | 10 | Yue Lingshan | 19 | F | 3 | NULL | 2 | Zhang Sanfeng | 94 | M | | 10 | Yue Lingshan | 19 | F | 3 | NULL | 3 | Miejue Shitai | 77 | F | | 10 | Yue Lingshan | 19 | F | 3 | NULL | 4 | Lin Chaoying | 93 | F | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | 1 | Song Jiang | 45 | M | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | 2 | Zhang Sanfeng | 94 | M | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | 3 | Miejue Shitai | 77 | F | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | 4 | Lin Chaoying | 93 | F | | 12 | Wen Qingqing | 19 | F | 1 | NULL | 1 | Song Jiang | 45 | M | | 12 | Wen Qingqing | 19 | F | 1 | NULL | 2 | Zhang Sanfeng | 94 | M | | 12 | Wen Qingqing | 19 | F | 1 | NULL | 3 | Miejue Shitai | 77 | F | | 12 | Wen Qingqing | 19 | F | 1 | NULL | 4 | Lin Chaoying | 93 | F | | 13 | Tian Boguang | 33 | M | 2 | NULL | 1 | Song Jiang | 45 | M | | 13 | Tian Boguang | 33 | M | 2 | NULL | 2 | Zhang Sanfeng | 94 | M | | 13 | Tian Boguang | 33 | M | 2 | NULL | 3 | Miejue Shitai | 77 | F | | 13 | Tian Boguang | 33 | M | 2 | NULL | 4 | Lin Chaoying | 93 | F | | 14 | Lu Wushuang | 17 | F | 3 | NULL | 1 | Song Jiang | 45 | M | | 14 | Lu Wushuang | 17 | F | 3 | NULL | 2 | Zhang Sanfeng | 94 | M | | 14 | Lu Wushuang | 17 | F | 3 | NULL | 3 | Miejue Shitai | 77 | F | | 14 | Lu Wushuang | 17 | F | 3 | NULL | 4 | Lin Chaoying | 93 | F | | 15 | Duan Yu | 19 | M | 4 | NULL | 1 | Song Jiang | 45 | M | | 15 | Duan Yu | 19 | M | 4 | NULL | 2 | Zhang Sanfeng | 94 | M | | 15 | Duan Yu | 19 | M | 4 | NULL | 3 | Miejue Shitai | 77 | F | | 15 | Duan Yu | 19 | M | 4 | NULL | 4 | Lin Chaoying | 93 | F | | 16 | Xu Zhu | 21 | M | 1 | NULL | 1 | Song Jiang | 45 | M | | 16 | Xu Zhu | 21 | M | 1 | NULL | 2 | Zhang Sanfeng | 94 | M | | 16 | Xu Zhu | 21 | M | 1 | NULL | 3 | Miejue Shitai | 77 | F | | 16 | Xu Zhu | 21 | M | 1 | NULL | 4 | Lin Chaoying | 93 | F | | 17 | Lin Chong | 25 | M | 4 | NULL | 1 | Song Jiang | 45 | M | | 17 | Lin Chong | 25 | M | 4 | NULL | 2 | Zhang Sanfeng | 94 | M | | 17 | Lin Chong | 25 | M | 4 | NULL | 3 | Miejue Shitai | 77 | F | | 17 | Lin Chong | 25 | M | 4 | NULL | 4 | Lin Chaoying | 93 | F | | 18 | Hua Rong | 23 | M | 7 | NULL | 1 | Song Jiang | 45 | M | | 18 | Hua Rong | 23 | M | 7 | NULL | 2 | Zhang Sanfeng | 94 | M | | 18 | Hua Rong | 23 | M | 7 | NULL | 3 | Miejue Shitai | 77 | F | | 18 | Hua Rong | 23 | M | 7 | NULL | 4 | Lin Chaoying | 93 | F | | 19 | Xue Baochai | 18 | F | 6 | NULL | 1 | Song Jiang | 45 | M | | 19 | Xue Baochai | 18 | F | 6 | NULL | 2 | Zhang Sanfeng | 94 | M | | 19 | Xue Baochai | 18 | F | 6 | NULL | 3 | Miejue Shitai | 77 | F | | 19 | Xue Baochai | 18 | F | 6 | NULL | 4 | Lin Chaoying | 93 | F | | 20 | Diao Chan | 19 | F | 7 | NULL | 1 | Song Jiang | 45 | M | | 20 | Diao Chan | 19 | F | 7 | NULL | 2 | Zhang Sanfeng | 94 | M | | 20 | Diao Chan | 19 | F | 7 | NULL | 3 | Miejue Shitai | 77 | F | | 20 | Diao Chan | 19 | F | 7 | NULL | 4 | Lin Chaoying | 93 | F | | 21 | Huang Yueying | 22 | F | 6 | NULL | 1 | Song Jiang | 45 | M | | 21 | Huang Yueying | 22 | F | 6 | NULL | 2 | Zhang Sanfeng | 94 | M | | 21 | Huang Yueying | 22 | F | 6 | NULL | 3 | Miejue Shitai | 77 | F | | 21 | Huang Yueying | 22 | F | 6 | NULL | 4 | Lin Chaoying | 93 | F | | 22 | Xiao Qiao | 20 | F | 1 | NULL | 1 | Song Jiang | 45 | M | | 22 | Xiao Qiao | 20 | F | 1 | NULL | 2 | Zhang Sanfeng | 94 | M | | 22 | Xiao Qiao | 20 | F | 1 | NULL | 3 | Miejue Shitai | 77 | F | | 22 | Xiao Qiao | 20 | F | 1 | NULL | 4 | Lin Chaoying | 93 | F | | 23 | Ma Chao | 23 | M | 4 | NULL | 1 | Song Jiang | 45 | M | | 23 | Ma Chao | 23 | M | 4 | NULL | 2 | Zhang Sanfeng | 94 | M | | 23 | Ma Chao | 23 | M | 4 | NULL | 3 | Miejue Shitai | 77 | F | | 23 | Ma Chao | 23 | M | 4 | NULL | 4 | Lin Chaoying | 93 | F | | 24 | Xu Xian | 27 | M | NULL | NULL | 1 | Song Jiang | 45 | M | | 24 | Xu Xian | 27 | M | NULL | NULL | 2 | Zhang Sanfeng | 94 | M | | 24 | Xu Xian | 27 | M | NULL | NULL | 3 | Miejue Shitai | 77 | F | | 24 | Xu Xian | 27 | M | NULL | NULL | 4 | Lin Chaoying | 93 | F | | 25 | Sun Dasheng | 100 | M | NULL | NULL | 1 | Song Jiang | 45 | M | | 25 | Sun Dasheng | 100 | M | NULL | NULL | 2 | Zhang Sanfeng | 94 | M | | 25 | Sun Dasheng | 100 | M | NULL | NULL | 3 | Miejue Shitai | 77 | F | | 25 | Sun Dasheng | 100 | M | NULL | NULL | 4 | Lin Chaoying | 93 | F | +-------+---------------+-----+--------+---------+-----------+-----+---------------+-----+--------+ 100 rows in set (0.00 sec) MariaDB [yinzhengjie]>
3>.内连接查询
等值连接：让表之间的字段以“等值”建立连接关系；
不等值连接
自然连接:去掉重复列的等值连接
自连接
MariaDB [yinzhengjie]> SELECT * FROM students; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+ 25 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM teachers; +-----+---------------+-----+--------+ | TID | Name | Age | Gender | +-----+---------------+-----+--------+ | 1 | Song Jiang | 45 | M | | 2 | Zhang Sanfeng | 94 | M | | 3 | Miejue Shitai | 77 | F | | 4 | Lin Chaoying | 93 | F | +-----+---------------+-----+--------+ 4 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM students,teachers WHERE students.TeacherID = teachers.TID; #该写法太老，不推荐使用 +-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+ | StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name | Age | Gender | +-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+ | 5 | Yu Yutong | 26 | M | 3 | 1 | 1 | Song Jiang | 45 | M | | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 3 | Miejue Shitai | 77 | F | | 4 | Ding Dian | 32 | M | 4 | 4 | 4 | Lin Chaoying | 93 | F | +-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+ 3 rows in set (0.00 sec) MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> SELECT * FROM students; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+ 25 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM teachers; +-----+---------------+-----+--------+ | TID | Name | Age | Gender | +-----+---------------+-----+--------+ | 1 | Song Jiang | 45 | M | | 2 | Zhang Sanfeng | 94 | M | | 3 | Miejue Shitai | 77 | F | | 4 | Lin Chaoying | 93 | F | +-----+---------------+-----+--------+ 4 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM students INNER JOIN teachers ON students.TeacherID = teachers.TID; #内连接查询，推荐使用该写法 +-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+ | StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name | Age | Gender | +-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+ | 5 | Yu Yutong | 26 | M | 3 | 1 | 1 | Song Jiang | 45 | M | | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 3 | Miejue Shitai | 77 | F | | 4 | Ding Dian | 32 | M | 4 | 4 | 4 | Lin Chaoying | 93 | F | +-------+-------------+-----+--------+---------+-----------+-----+---------------+-----+--------+ 3 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> SELECT * FROM students; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+ 25 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM teachers; +-----+---------------+-----+--------+ | TID | Name | Age | Gender | +-----+---------------+-----+--------+ | 1 | Song Jiang | 45 | M | | 2 | Zhang Sanfeng | 94 | M | | 3 | Miejue Shitai | 77 | F | | 4 | Lin Chaoying | 93 | F | +-----+---------------+-----+--------+ 4 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT stuid,s.name AS 学生姓名 ,tid,t.name AS 老师姓名 FROM students AS s INNER JOIN teachers AS t ON s.TeacherID = t.TID; #查询制定者字段并设置字段别名,也为表名设置别名进行调用。 +-------+--------------+-----+---------------+ | stuid | 学生姓名 | tid | 老师姓名 | +-------+--------------+-----+---------------+ | 5 | Yu Yutong | 1 | Song Jiang | | 1 | Shi Zhongyu | 3 | Miejue Shitai | | 4 | Ding Dian | 4 | Lin Chaoying | +-------+--------------+-----+---------------+ 3 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> CREATE TABLE emp(id int,name char(3),leaderid int); Query OK, 0 rows affected (0.01 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> DESC emp; +----------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +----------+---------+------+-----+---------+-------+ | id | int(11) | YES | | NULL | | | name | char(3) | YES | | NULL | | | leaderid | int(11) | YES | | NULL | | +----------+---------+------+-----+---------+-------+ rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> INSERT INTO emp VALUES(1,'张无忌',null),(2,'杨逍',1),(3,'范遥',2),(4,'殷天正',2),(5,'韦一笑',2); Query OK, 5 rows affected (0.00 sec) Records: 5 Duplicates: 0 Warnings: 0 MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM emp; +------+-----------+----------+ | id | name | leaderid | +------+-----------+----------+ | 1 | 张无忌 | NULL | | 2 | 杨逍 | 1 | | 3 | 范遥 | 2 | | 4 | 殷天正 | 2 | | 5 | 韦一笑 | 2 | +------+-----------+----------+ rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT a.name,b.name AS 领导 FROM emp AS a LEFT OUTER JOIN emp AS b ON a.leaderid = b.id; #同一张表查询数据，查询每个人及其领导的姓名。(自连接查询) +-----------+-----------+ | name | 领导 | +-----------+-----------+ | 杨逍 | 张无忌 | | 范遥 | 杨逍 | | 殷天正 | 杨逍 | | 韦一笑 | 杨逍 | | 张无忌 | NULL | +-----------+-----------+ rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]>
4>.子查询
子查询：在查询语句嵌套着查询语句，性能较差
基于某语句的查询结果再次进行的查询
用在WHERE子句中的子查询
用于比较表达式中的子查询；子查询仅能返回单个值
SELECT Name,Age FROM students WHERE Age>(SELECT avg(Age) FROM students);
用于IN中的子查询：子查询应该单键查询并返回一个或多个值从构成列表
SELECT Name,Age FROM students WHERE Age IN (SELECT Age FROM teachers);
用于EXISTS
用于FROM子句中的子查询
使用格式：SELECT tb_alias.col1,... FROM (SELECT clause) AS tb_alias WHERE Clause;
示例：
SELECT s.aage,s.ClassID FROM (SELECT avg(Age) AS aage,ClassID FROM students WHERE ClassID IS NOT NULL GROUP BY ClassID) AS s WHERE s.aage>30;
MariaDB [yinzhengjie]> SELECT AVG(age) FROM students; +----------+ | AVG(age) | +----------+ | 27.4000 | +----------+ row in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM teachers; +-----+---------------+-----+--------+ | TID | Name | Age | Gender | +-----+---------------+-----+--------+ | 1 | Song Jiang | 45 | M | | 2 | Zhang Sanfeng | 94 | M | | 3 | Miejue Shitai | 77 | F | | 4 | Lin Chaoying | 93 | F | +-----+---------------+-----+--------+ rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM teachers WHERE age > (SELECT AVG(age) FROM students) * 2; +-----+---------------+-----+--------+ | TID | Name | Age | Gender | +-----+---------------+-----+--------+ | 2 | Zhang Sanfeng | 94 | M | | 3 | Miejue Shitai | 77 | F | | 4 | Lin Chaoying | 93 | F | +-----+---------------+-----+--------+ rows in set (0.00 sec) MariaDB [yinzhengjie]>
5>.外连接查询
左外连接： FROM tb1 LEFT JOIN tb2 ON tb1.col=tb2.col
右外连接 FROM tb1 RIGHT JOIN tb2 ON tb1.col=tb2.col
MariaDB [yinzhengjie]> SELECT * FROM teachers; +-----+---------------+-----+--------+ | TID | Name | Age | Gender | +-----+---------------+-----+--------+ | 1 | Song Jiang | 45 | M | | 2 | Zhang Sanfeng | 94 | M | | 3 | Miejue Shitai | 77 | F | | 4 | Lin Chaoying | 93 | F | +-----+---------------+-----+--------+ 4 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM students; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+ 25 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM students AS s LEFT OUTER JOIN teachers AS t ON s.TeacherID = t.TID; #左外连接，以students表(在左边)记录为校验 +-------+---------------+-----+--------+---------+-----------+------+---------------+------+--------+ | StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name | Age | Gender | +-------+---------------+-----+--------+---------+-----------+------+---------------+------+--------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 3 | Miejue Shitai | 77 | F | | 2 | Shi Potian | 22 | M | 1 | 7 | NULL | NULL | NULL | NULL | | 3 | Xie Yanke | 53 | M | 2 | 16 | NULL | NULL | NULL | NULL | | 4 | Ding Dian | 32 | M | 4 | 4 | 4 | Lin Chaoying | 93 | F | | 5 | Yu Yutong | 26 | M | 3 | 1 | 1 | Song Jiang | 45 | M | | 6 | Shi Qing | 46 | M | 5 | NULL | NULL | NULL | NULL | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | NULL | NULL | NULL | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | NULL | NULL | NULL | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | NULL | NULL | NULL | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | NULL | NULL | NULL | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | NULL | NULL | NULL | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | NULL | NULL | NULL | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | NULL | NULL | NULL | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | NULL | NULL | NULL | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | NULL | NULL | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | NULL | NULL | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+------+---------------+------+--------+ 25 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> SELECT * FROM teachers; +-----+---------------+-----+--------+ | TID | Name | Age | Gender | +-----+---------------+-----+--------+ | 1 | Song Jiang | 45 | M | | 2 | Zhang Sanfeng | 94 | M | | 3 | Miejue Shitai | 77 | F | | 4 | Lin Chaoying | 93 | F | +-----+---------------+-----+--------+ 4 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM students; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+ 25 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM students AS s RIGHT OUTER JOIN teachers AS t ON s.TeacherID = t.TID; #右外连接,以"teachers"(在右边)表记录为校验 +-------+-------------+------+--------+---------+-----------+-----+---------------+-----+--------+ | StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name | Age | Gender | +-------+-------------+------+--------+---------+-----------+-----+---------------+-----+--------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 3 | Miejue Shitai | 77 | F | | 4 | Ding Dian | 32 | M | 4 | 4 | 4 | Lin Chaoying | 93 | F | | 5 | Yu Yutong | 26 | M | 3 | 1 | 1 | Song Jiang | 45 | M | | NULL | NULL | NULL | NULL | NULL | NULL | 2 | Zhang Sanfeng | 94 | M | +-------+-------------+------+--------+---------+-----------+-----+---------------+-----+--------+ 4 rows in set (0.00 sec) MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> SELECT * FROM students AS s LEFT OUTER JOIN teachers AS t ON s.TeacherID = t.TID; +-------+---------------+-----+--------+---------+-----------+------+---------------+------+--------+ | StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name | Age | Gender | +-------+---------------+-----+--------+---------+-----------+------+---------------+------+--------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 3 | Miejue Shitai | 77 | F | | 2 | Shi Potian | 22 | M | 1 | 7 | NULL | NULL | NULL | NULL | | 3 | Xie Yanke | 53 | M | 2 | 16 | NULL | NULL | NULL | NULL | | 4 | Ding Dian | 32 | M | 4 | 4 | 4 | Lin Chaoying | 93 | F | | 5 | Yu Yutong | 26 | M | 3 | 1 | 1 | Song Jiang | 45 | M | | 6 | Shi Qing | 46 | M | 5 | NULL | NULL | NULL | NULL | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | NULL | NULL | NULL | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | NULL | NULL | NULL | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | NULL | NULL | NULL | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | NULL | NULL | NULL | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | NULL | NULL | NULL | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | NULL | NULL | NULL | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | NULL | NULL | NULL | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | NULL | NULL | NULL | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | NULL | NULL | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | NULL | NULL | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+------+---------------+------+--------+ 25 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM students AS s LEFT OUTER JOIN teachers AS t ON s.TeacherID = t.TID WHERE t.tid IS NULL; #对左外连接再次进行过滤，将两个表中重复的数据剔除。 +-------+---------------+-----+--------+---------+-----------+------+------+------+--------+ | StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name | Age | Gender | +-------+---------------+-----+--------+---------+-----------+------+------+------+--------+ | 2 | Shi Potian | 22 | M | 1 | 7 | NULL | NULL | NULL | NULL | | 3 | Xie Yanke | 53 | M | 2 | 16 | NULL | NULL | NULL | NULL | | 6 | Shi Qing | 46 | M | 5 | NULL | NULL | NULL | NULL | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | NULL | NULL | NULL | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | NULL | NULL | NULL | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | NULL | NULL | NULL | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | NULL | NULL | NULL | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | NULL | NULL | NULL | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | NULL | NULL | NULL | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | NULL | NULL | NULL | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | NULL | NULL | NULL | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | NULL | NULL | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | NULL | NULL | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+------+------+------+--------+ 22 rows in set (0.00 sec) MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> SELECT * FROM teachers; +-----+---------------+-----+--------+ | TID | Name | Age | Gender | +-----+---------------+-----+--------+ | 1 | Song Jiang | 45 | M | | 2 | Zhang Sanfeng | 94 | M | | 3 | Miejue Shitai | 77 | F | | 4 | Lin Chaoying | 93 | F | +-----+---------------+-----+--------+ 4 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM students; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+ 25 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM students AS s RIGHT OUTER JOIN teachers AS t ON s.TeacherID = t.TID; +-------+-------------+------+--------+---------+-----------+-----+---------------+-----+--------+ | StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name | Age | Gender | +-------+-------------+------+--------+---------+-----------+-----+---------------+-----+--------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 3 | Miejue Shitai | 77 | F | | 4 | Ding Dian | 32 | M | 4 | 4 | 4 | Lin Chaoying | 93 | F | | 5 | Yu Yutong | 26 | M | 3 | 1 | 1 | Song Jiang | 45 | M | | NULL | NULL | NULL | NULL | NULL | NULL | 2 | Zhang Sanfeng | 94 | M | +-------+-------------+------+--------+---------+-----------+-----+---------------+-----+--------+ 4 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM students AS s RIGHT OUTER JOIN teachers AS t ON s.TeacherID = t.TID WHERE s.teacherid IS NULL; #对右外连接再次进行过滤，将重复的数据剔除掉。 +-------+------+------+--------+---------+-----------+-----+---------------+-----+--------+ | StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name | Age | Gender | +-------+------+------+--------+---------+-----------+-----+---------------+-----+--------+ | NULL | NULL | NULL | NULL | NULL | NULL | 2 | Zhang Sanfeng | 94 | M | +-------+------+------+--------+---------+-----------+-----+---------------+-----+--------+ 1 row in set (0.00 sec) MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> SELECT * FROM teachers; +-----+---------------+-----+--------+ | TID | Name | Age | Gender | +-----+---------------+-----+--------+ | 1 | Song Jiang | 45 | M | | 2 | Zhang Sanfeng | 94 | M | | 3 | Miejue Shitai | 77 | F | | 4 | Lin Chaoying | 93 | F | +-----+---------------+-----+--------+ 4 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM students; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+ 25 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM students AS s FULL OUTER JOIN teachers AS t ON s.teacherid = t.tid; #MySQL/MariaDB不支持完全外连接查询 ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax t o use near 'FULL OUTER JOIN teachers AS t ON s.teacherid = t.tid' at line 1 MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM students AS s LEFT OUTER JOIN teachers AS t ON s.TeacherID = t.TID UNION SELECT * FROM students AS s RIGHT O UTER JOIN teachers AS t ON s.TeacherID = t.TID; #由于MySQL/MariaDB不支持完全外连接查询，但是我们可以使用左外连接与右外连接的查询结果通过UNION去重功能实现完全外连接查询功能。 +-------+---------------+------+--------+---------+-----------+------+---------------+------+--------+ | StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name | Age | Gender | +-------+---------------+------+--------+---------+-----------+------+---------------+------+--------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 3 | Miejue Shitai | 77 | F | | 2 | Shi Potian | 22 | M | 1 | 7 | NULL | NULL | NULL | NULL | | 3 | Xie Yanke | 53 | M | 2 | 16 | NULL | NULL | NULL | NULL | | 4 | Ding Dian | 32 | M | 4 | 4 | 4 | Lin Chaoying | 93 | F | | 5 | Yu Yutong | 26 | M | 3 | 1 | 1 | Song Jiang | 45 | M | | 6 | Shi Qing | 46 | M | 5 | NULL | NULL | NULL | NULL | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | NULL | NULL | NULL | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | NULL | NULL | NULL | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | NULL | NULL | NULL | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | NULL | NULL | NULL | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | NULL | NULL | NULL | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | NULL | NULL | NULL | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | NULL | NULL | NULL | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | NULL | NULL | NULL | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | NULL | NULL | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | NULL | NULL | NULL | NULL | | NULL | NULL | NULL | NULL | NULL | NULL | 2 | Zhang Sanfeng | 94 | M | +-------+---------------+------+--------+---------+-----------+------+---------------+------+--------+ 26 rows in set (0.00 sec) MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> SELECT * FROM students; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+ 25 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM teachers; +-----+---------------+-----+--------+ | TID | Name | Age | Gender | +-----+---------------+-----+--------+ | 1 | Song Jiang | 45 | M | | 2 | Zhang Sanfeng | 94 | M | | 3 | Miejue Shitai | 77 | F | | 4 | Lin Chaoying | 93 | F | +-----+---------------+-----+--------+ 4 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM (SELECT stuid,s.name AS student_name,s.age AS student_age,s.gender AS student_gender,classid,teacherid,tid,t.name AS teacher_name,t.age AS teacher_age,t.gender AS teacher_gender FROM students AS s LEFT OUTER JOIN teachers AS t ON s.TeacherID = t.TID UNION SELECT stuid,s.name AS student_name,s.age AS student_age,s.gender AS student_gender,classid,teacherid,tid,t.name AS teacher_name,t.age AS teacher_age,t.gender AS teacher_gender FROM students AS s RIGHT OUTER JOIN teachers AS t ON s.TeacherID = t.TID) AS f WHERE f.teacherid IS NULL OR f.tid IS NULL; #将间接实现完全外连接查询结果再次进行过滤,查询出完全外连接中过滤掉两表重复的数据。 +-------+---------------+-------------+----------------+---------+-----------+------+---------------+-------------+----------------+ | stuid | student_name | student_age | student_gender | classid | teacherid | tid | teacher_name | teacher_age | teacher_gender | +-------+---------------+-------------+----------------+---------+-----------+------+---------------+-------------+----------------+ | 2 | Shi Potian | 22 | M | 1 | 7 | NULL | NULL | NULL | NULL | | 3 | Xie Yanke | 53 | M | 2 | 16 | NULL | NULL | NULL | NULL | | 6 | Shi Qing | 46 | M | 5 | NULL | NULL | NULL | NULL | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | NULL | NULL | NULL | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | NULL | NULL | NULL | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | NULL | NULL | NULL | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | NULL | NULL | NULL | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | NULL | NULL | NULL | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | NULL | NULL | NULL | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | NULL | NULL | NULL | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | NULL | NULL | NULL | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | NULL | NULL | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | NULL | NULL | NULL | NULL | | NULL | NULL | NULL | NULL | NULL | NULL | 2 | Zhang Sanfeng | 94 | M | +-------+---------------+-------------+----------------+---------+-----------+------+---------------+-------------+----------------+ 23 rows in set (0.00 sec) MariaDB [yinzhengjie]>
6>.自连接查询
MariaDB [yinzhengjie]> CREATE TABLE emp(id int,name char(3),leaderid int); Query OK, 0 rows affected (0.01 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> DESC emp; +----------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +----------+---------+------+-----+---------+-------+ | id | int(11) | YES | | NULL | | | name | char(3) | YES | | NULL | | | leaderid | int(11) | YES | | NULL | | +----------+---------+------+-----+---------+-------+ rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> INSERT INTO emp VALUES(1,'张无忌',null),(2,'杨逍',1),(3,'范遥',2),(4,'殷天正',2),(5,'韦一笑',2); Query OK, 5 rows affected (0.00 sec) Records: 5 Duplicates: 0 Warnings: 0 MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT * FROM emp; +------+-----------+----------+ | id | name | leaderid | +------+-----------+----------+ | 1 | 张无忌 | NULL | | 2 | 杨逍 | 1 | | 3 | 范遥 | 2 | | 4 | 殷天正 | 2 | | 5 | 韦一笑 | 2 | +------+-----------+----------+ rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]> SELECT a.name,b.name AS 领导 FROM emp AS a LEFT OUTER JOIN emp AS b ON a.leaderid = b.id; #同一张表查询数据，查询每个人及其领导的姓名。 +-----------+-----------+ | name | 领导 | +-----------+-----------+ | 杨逍 | 张无忌 | | 范遥 | 杨逍 | | 殷天正 | 杨逍 | | 韦一笑 | 杨逍 | | 张无忌 | NULL | +-----------+-----------+ 5 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]>
三.SELECT语句(单表操作)执行流程
四.小试牛刀(本案例使用3张表，仍基于上面导入的"yinzhengjie_innodb.sql"数据进行演示)
MariaDB [yinzhengjie]> SELECT * FROM students; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+ 25 rows in set (0.00 sec) MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> SELECT * FROM courses; +----------+----------------+ | CourseID | Course | +----------+----------------+ | 1 | Hamo Gong | | 2 | Kuihua Baodian | | 3 | Jinshe Jianfa | | 4 | Taiji Quan | | 5 | Daiyu Zanghua | | 6 | Weituo Zhang | | 7 | Dagou Bangfa | +----------+----------------+ 7 rows in set (0.01 sec) MariaDB [yinzhengjie]>
MariaDB [yinzhengjie]> SELECT * FROM scores; +----+-------+----------+-------+ | ID | StuID | CourseID | Score | +----+-------+----------+-------+ | 1 | 1 | 2 | 77 | | 2 | 1 | 6 | 93 | | 3 | 2 | 2 | 47 | | 4 | 2 | 5 | 97 | | 5 | 3 | 2 | 88 | | 6 | 3 | 6 | 75 | | 7 | 4 | 5 | 71 | | 8 | 4 | 2 | 89 | | 9 | 5 | 1 | 39 | | 10 | 5 | 7 | 63 | | 11 | 6 | 1 | 96 | | 12 | 7 | 1 | 86 | | 13 | 7 | 7 | 83 | | 14 | 8 | 4 | 57 | | 15 | 8 | 3 | 93 | +----+-------+----------+-------+ 15 rows in set (0.00 sec) MariaDB [yinzhengjie]>
1>.查询学生姓名，考试科目以及对应的成绩
MariaDB [yinzhengjie]> SELECT a.name AS 姓名,c.course AS 课程,b.score AS 分数 FROM students AS a INNER JOIN scores AS b ON a.stuid = b.id INNER JOIN courses AS c ON b.courseid = c.courseid; +---------------+----------------+--------+ | 姓名 | 课程 | 分数 | +---------------+----------------+--------+ | Shi Zhongyu | Kuihua Baodian | 77 | | Shi Potian | Weituo Zhang | 93 | | Xie Yanke | Kuihua Baodian | 47 | | Ding Dian | Daiyu Zanghua | 97 | | Yu Yutong | Kuihua Baodian | 88 | | Shi Qing | Weituo Zhang | 75 | | Xi Ren | Daiyu Zanghua | 71 | | Lin Daiyu | Kuihua Baodian | 89 | | Ren Yingying | Hamo Gong | 39 | | Yue Lingshan | Dagou Bangfa | 63 | | Yuan Chengzhi | Hamo Gong | 96 | | Wen Qingqing | Hamo Gong | 86 | | Tian Boguang | Dagou Bangfa | 83 | | Lu Wushuang | Taiji Quan | 57 | | Duan Yu | Jinshe Jianfa | 93 | +---------------+----------------+--------+ 15 rows in set (0.00 sec) MariaDB [yinzhengjie]> MariaDB [yinzhengjie]>
2>.以ClassID分组，显示每班的同学的人数
3>.以Gender分组，显示其年龄之和
4>.以ClassID分组，显示其平均年龄大于25的班级
5>.以Gender分组，显示各组中年龄大于25的学员的年龄之和
6>.显示前5位同学的姓名、课程及成绩
7>.显示其成绩高于80的同学的名称及课程
8>.取每位同学各门课的平均成绩，显示成绩前三名的同学的姓名和平均成绩
9>.显示每门课程课程名称及学习了这门课的同学的个数
10>.显示其年龄大于平均年龄的同学的名字
11>.显示其学习的课程为第1、2，4或第7门课的同学的名字
12>.显示其成员数最少为3个的班级的同学中年龄大于同班同学平均年龄的同学
13>.统计各班级中年龄大于全校同学平均年龄的同学