语法：
UPDATE [LOW_PRIORITY] [IGNORE] table_reference SET col_name1={expr1 | DEFAULT} [, col_name2={expr2 | DEFAULT}]... [WHERE where_condition]
eg：
UPDATE users SET age = age + 5, sex = 2 WHERE username='TOM';
增insert
删delete
改update
查SELECT
### 删除记录（单表删除）
如果省略WHERE，则该表所有记录都将被删除
DELETE FROM table_name [WHERE where_condition]
### 删除表：
DROP TABLE table_name;
删除没有被关联的普通表：直接上面的SQL语句就行了
删除被其他表关联的父表：
- 方法一：先删除子表，再删除父表
- 方法二：先删除父表的外键约束，再删除父表
SELECT id username FROM users 等于 SELECT id as username FROM users
查询记录中的usename和ID
mysql> SELECT usename,id FROM users25; //记录将以usename,id顺序来进行显示
使用as来进行赋予别名
mysql> SELECT id AS userID,usename AS Uname FROM users25;//记录将以userID,Uname顺序来进行显示
stand by 分组查询
+----+---------+----------+-----+------+
| id | usename | password | age | sex |
+----+---------+----------+-----+------+
| 1 | TOM | 123 | 29 | 0 |
| 2 | JOHN | 456 | 38 | 0 |
| 3 | JOHN | 456 | 27 | 0 |
| 4 | JOHN | 456 | 36 | 0 |
| 7 | TIM | 222 | 42 | 1 |
+----+---------+----------+-----+------+
5 rows in set (0.00 sec)
mysql> SELECT sex FROM users25 GROUP BY sex; //对sex进行分组查询
+------+
| sex |
+------+
| 0 |
| 1 |
+------+
-
select * from 数据表名 ORDER BY 字段;//通过某个字段进行升序排列
-
select * from 数据表名 ORDER BY 某一个字段 DESC
