mysql利于cte进行分组统计并计算占比

CTE定义：一个公共表表达式（common table expression）是一个命名的临时结果集，它在一条单独的语句中有效，可以在语句中被引用多次。

CTE基本语法：

WITH
  cte1 [(col_name [, col_name] ...)] AS (SELECT a, b FROM table1),
  cte2 [(col_name [, col_name] ...)] AS (SELECT c, d FROM table2)
SELECT b, d FROM cte1 JOIN cte2
WHERE cte1.a = cte2.c;

CTE好处：

1. 可以在一条语句中被引用多次。
2. 可以递归引用（自引用）。
3. 可以相互引用。
4. 可读性好。

参考：WITH Syntax (Common Table Expressions)

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备注：cte只能在mysql8.0及以上版本中使用。

测试数据表sql：books.sql

-- MySQL dump 10.13  Distrib 5.7.23, for linux-glibc2.12 (x86_64)
--
-- Host: localhost    Database: mydb
-- ------------------------------------------------------
-- Server version       5.7.23-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 */;

--
-- Table structure for table `books`
--

DROP TABLE IF EXISTS `books`;
/*!40101 SET @saved_cs_client     = @@character_set_client */;
/*!40101 SET character_set_client = utf8 */;
CREATE TABLE `books` (
  `bno` varchar(32) DEFAULT NULL COMMENT '书号',
  `bname` varchar(64) DEFAULT NULL COMMENT '书名',
  `author` varchar(32) DEFAULT NULL COMMENT '作者',
  `price` double DEFAULT NULL COMMENT '单价'
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
/*!40101 SET character_set_client = @saved_cs_client */;

--
-- Dumping data for table `books`
--

LOCK TABLES `books` WRITE;
/*!40000 ALTER TABLE `books` DISABLE KEYS */;
INSERT INTO `books` VALUES ('1001','definitive sql','wanger',61),('1002','java programming','wanger',45),('1003','shell programming','wanger',28),('1004','scala programming','lisi',32),('1005','c programming','lisi',66);
/*!40000 ALTER TABLE `books` 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 2018-11-06 18:29:35

在mysql命令行中导入数据：mysql> source /path/books.sql;

mysql> with temp(booknum) as (select count(*) from books) select author,count(author)/(select booknum from temp) from books group by author;

输出如下：