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1.插入操作 INSERT
（1）INSERT table_name（col_name,...） VALUES(...),(....)
CREATE TABLE user( id SMALLINT UNSIGNED PRIMARY KEY AUTO_INCREMENT, username VARCHAR(20) NOT NULL, password VARCHAR(32) NOT NULL, age TINYINT UNSIGNED NOT DEFAULT 10, sex BOOLEAN );
为表插入数据
INSERT user VALUE(NULL,'JACK','123',25,1);
(2)可使用子查询插入
INSERT user(username) SELECT username FROM user WHERE age>30
INSERT user SET username='Den',password='123';
(3)INSERT table_name SELECT...
2.更新记录(单表更新) UPDATE
UPDATE table_name SET col_name=值 WHERE ID=..
3.删除记录(单表删除) DELETE
DELETE FROM table_name WHERE ...
4.查找记录 SELECT
SELECT * FROM table_name
(1).为字段取别名
SELECT username AS name FROM user AS u;
(2).WHRER对子路进行过滤，没有WHREE自居，则显示所有记录。在WHERE表达式，支持函数或运算符
SELECT username FROM user WHERE id = 3
(3).对查询的结果分组 GROUP BY
SELECT * FROM user GROUP BY sex;
(4).having语句设置分组条件,分组的条件如果不是聚合函数，必须出现在SELECT的语句当中。
SELECT * FROM user GROUP BY sex HAVING age>15
(5).对查询的结果进行排序 ASC升序，DESC倒叙
SELECT * FROM user ORDER BY id DESC
(6).limit限制查询结果返回数量 分页公式(当前页码-1) *每页显示的记录数
SELECT * FROM user limit 0,2
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