数据库(mysql5.5)的一些基本的操作

//创建一个数据库 school

CREATE DATABASE school;
//查看所有数据库
SHOW DATABASES;
USE school;
//创建第一个表 qy97;
CREATE TABLE qy97(id INT(10) PRIMARY KEY AUTO_INCREMENT,sname VARCHAR(10));
//查询创建的表
SELECT * FROM qy97;
DESC qy97;
SHOW TABLES;
//向表中添加字段
ALTER TABLE qy97 ADD age INT(20);
ALTER TABLE qy97 ADD addr VARCHAR(20);
SELECT * FROM qy97;
DESC qy97;
//修改表中字段名
ALTER TABLE qy97 CHANGE addr grade VARCHAR(10);
DESC qy97;
//修改字段类型
ALTER TABLE qy97 MODIFY grade INT(10);
DESC qy97;
//删除主键 首先把主键自增删除
ALTER TABLE qy97 MODIFY id INT NOT NULL;
DESC qy97;
ALTER TABLE qy97 DROP PRIMARY KEY ;
DESC qy97;
//添加主键
ALTER TABLE qy97 MODIFY id INT PRIMARY KEY;
DESC qy97;
//添加id自增
ALTER TABLE qy97 MODIFY id INT AUTO_INCREMENT;
DESC qy97;
//重命名表名
RENAME TABLE qy97 TO class1;
DESC class1;
ALTER TABLE class1 RENAME class2;
SHOW TABLES;
DESC class2;
//删除表中的字段
ALTER TABLE class2 DROP grade;
//向表中添加数据
INSERT INTO class2 VALUES (1,'韩高峰',20);
SELECT * FROM class2;
INSERT INTO class2 (sname,age) VALUES('杨蒙蒙',19);
INSERT INTO class2 (sname, age) VALUES ('胡歌',30);
INSERT INTO class2 (sname ,age) VALUES ('贾玲',35);
INSERT INTO class2 (sname,age) VALUES ('胡歌',35);
INSERT INTO class2 (sname,age) VALUES ('李易峰',30);
INSERT INTO class2 (sname, age) VALUES(NULL,NULL);
//修改表中数据
UPDATE class2 SET age = 40;
SELECT * FROM class2;
UPDATE class2 SET age = 19 WHERE sname ='杨蒙蒙';
UPDATE class2 SET age = 20 WHERE id = 1;
UPDATE class2 SET age = 30 WHERE age BETWEEN 35 AND 45;
UPDATE class2 SET sname= '李易峰'WHERE age = 30 AND sname = '胡歌';
//查空 IS NULL /IS NOT NULL;
SELECT * FROM class2 WHERE sname OR age IS NULL;
SELECT * FROM class2 WHERE (sname AND age) IS NULL;
SELECT * FROM class2 WHERE (sname AND age)IS NOT NULL;
//去重查询 SELECT DISTINCT 字段名 FROM 表名
SELECT DISTINCT sname FROM class2;
//别名查询 AS
SELECT sname AS '姓名' FROM class2;
SELECT id AS '编号' FROM class2;
SELECT age AS '年龄' FROM class2;
//模糊查询 LIKE
SELECT * FROM class2 WHERE sname LIKE '%李%';
SELECT * FROM class2 WHERE sname LIKE '___';
//排序 降序DESC 升序 ASC
SELECT *FROM class2 ORDER BY id DESC;
SELECT * FROM class2 ORDER BY id ASC;
SELECT * FROM class2 ORDER BY age ASC;
SELECT * FROM class2 ORDER BY id DESC;
//聚合函数 总行数
SELECT COUNT(*)AS '总行数' FROM class2;
SELECT * FROM class2;
//MIN AS别名(可写可不写)
SELECT id 'id', sname '姓名',MIN(age) '年龄最小' FROM class2;
//MAX 最大值
SELECT id AS 'id',sname AS '姓名', MAX(age) AS '年龄最大' FROM class2;
//AVG 平均值
SELECT id ,sname AS '姓名',AVG(age) AS '平均年龄' FROM class2;
// SUM 总和
SELECT id , sname AS '姓名', SUM(age) AS '年龄总和' FROM class2;