数据操纵语言（DML）
-
insert: 向表中插入数据
-
delete: 删除表中的数据，格式：delete from tablname [ where 条件 ]
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update: 修改表中的数据，格式：update tablname set colName1=value1[colName2=value2] [ where 条件 ]
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where: 对表中的数据增加条件进行限制，起到过滤的作用
- 格式：where colName 关系运算符 value [or|and 条件2]
- 关系运算符：> >= < <= 等于: = 不等于: != 或者 <>
-
null值操作: 比较null时，不能使用=或者!=或者<>, 而是使用 is 或者 is not ，在select子句中，使用关系运算符.
操作
创建一个表
### 创建 表
mysql> create table user(
-> id int,
-> name varchar(20),
-> birth date,
-> age int,
-> address varchar(50)
-> );
Query OK, 0 rows affected (0.01 sec)
### 查看 表结构
mysql> desc user;
字段 类型 是否允许为空 不写默认为空
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| name | varchar(20) | YES | | NULL | |
| birth | date | YES | | NULL | |
| age | int(11) | YES | | NULL | |
| address | varchar(50) | YES | | NULL | |
+---------+-------------+------+-----+---------+-------+
5 rows in set (0.00 sec)
插入数据
### 单个插入
mysql> insert into user values (1,'wangj',0122,22,'wuhan');
Query OK, 1 row affected (0.00 sec)
### 查看
mysql> select * from user;
+------+-------+------------+------+---------+
| id | name | birth | age | address |
+------+-------+------------+------+---------+
| 1 | wangj | 2000-01-22 | 22 | wuhan |
+------+-------+------------+------+---------+
1 row in set (0.00 sec)
### 批量插入
mysql> insert into user(id,name,address) values(2,'liuyww','wuhan'),
-> (3,'wangx','wenzhou'),
-> (4,'test','test');
Query OK, 3 rows affected (0.01 sec)
Records: 3 Duplicates: 0 Warnings: 0
### 查看
mysql> select * from user;
+------+--------+------------+------+---------+
| id | name | birth | age | address |
+------+--------+------------+------+---------+
| 1 | wangj | 2000-01-22 | 22 | wuhan |
| 2 | liuyww | NULL | NULL | wuhan |
| 3 | wangx | NULL | NULL | wenzhou |
| 4 | test | NULL | NULL | test |
+------+--------+------------+------+---------+
4 rows in set (0.01 sec)
删除数据
### where 删除
mysql> delete from user where id='4';
Query OK, 1 row affected (0.00 sec)
### 查看
mysql> select * from user;
+------+--------+------------+------+---------+
| id | name | birth | age | address |
+------+--------+------------+------+---------+
| 1 | wangj | 2000-01-22 | 22 | wuhan |
| 2 | liuyww | NULL | NULL | wuhan |
| 3 | wangx | NULL | NULL | wenzhou |
+------+--------+------------+------+---------+
3 rows in set (0.00 sec)
### where and 删除
mysql> delete from user where id='1' and address='suzhou'; ### 满足两项条件的匹配数据会被删除 [ and 等同于 并且 ]
Query OK, 0 rows affected (0.01 sec)
mysql> select * from user; ### 未删除成功 [ 不存在同时满足上述两项条件的数据 ]
+------+--------+------------+------+---------+
| id | name | birth | age | address |
+------+--------+------------+------+---------+
| 1 | wangj | 2000-01-22 | 22 | wuhan |
| 2 | liuyww | NULL | NULL | wuhan |
| 3 | wangx | NULL | NULL | wenzhou |
+------+--------+------------+------+---------+
3 rows in set (0.00 sec)
mysql> delete from user where id='1' and address='wuhan'; ### 匹配到满足两项条件的数据
Query OK, 1 row affected (0.00 sec)
mysql> select * from user; ### 删除成功
+------+--------+-------+------+---------+
| id | name | birth | age | address |
+------+--------+-------+------+---------+
| 2 | liuyww | NULL | NULL | wuhan |
| 3 | wangx | NULL | NULL | wenzhou |
+------+--------+-------+------+---------+
2 rows in set (0.00 sec)
### where or 删除
mysql> delete from user where id='4' or address='wuhan'; ### 满足其中一项条件的数据会被匹配删除；[ or 等同于 或者 ]
Query OK, 1 row affected (0.01 sec)
mysql> select * from user; ### address等于武汉的数据已被删除
+------+-------+-------+------+---------+
| id | name | birth | age | address |
+------+-------+-------+------+---------+
| 3 | wangx | NULL | NULL | wenzhou |
+------+-------+-------+------+---------+
1 row in set (0.00 sec)
### 直接删除所有数据 [ 不加where 条件 ]
mysql> delete from user; ### 不加 where 条件 刪除所有数据
Query OK, 4 rows affected (0.00 sec)
mysql> select * from user; ### user 中所有数据已被删除
Empty set (0.00 sec)
更新数据
### 整体更新
mysql> update user set address='china'; ### 将user表中所有数据地址更新为China
Query OK, 3 rows affected (0.01 sec)
Rows matched: 3 Changed: 3 Warnings: 0
mysql> select * from user; ### 更新成功
+------+--------+-------+------+---------+
| id | name | birth | age | address |
+------+--------+-------+------+---------+
| 2 | liuyww | NULL | NULL | china |
| 3 | wangx | NULL | NULL | china |
| 4 | test | NULL | NULL | china |
+------+--------+-------+------+---------+
3 rows in set (0.00 sec)
### 单个更新
mysql> update user set address='wuhan',name='wangj' where id='4'; ### 将user表中id为4的数据 地址和名字更新为wuhan wangj
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from user; ### 更新成功
+------+--------+-------+------+---------+
| id | name | birth | age | address |
+------+--------+-------+------+---------+
| 2 | liuyww | NULL | NULL | china |
| 3 | wangx | NULL | NULL | china |
| 4 | wangj | NULL | NULL | wuhan |
+------+--------+-------+------+---------+
3 rows in set (0.00 sec)