【SQL】（MySQL）DML——UPDATE

選取表的信息：

+--------+-------------+------+-----+---------+-------+
| Field  | Type        | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+-------+
| number | char(11)    | YES  |     | NULL    |       |
| name   | varchar(50) | YES  |     | NULL    |       |
| age    | int(11)     | YES  |     | NULL    |       |
+--------+-------------+------+-----+---------+-------+

+--------+--------+------+
| number | name   | age  |
+--------+--------+------+
| 1      | java   |   25 |
| 2      | c      | NULL |
| NULL   | python |   29 |
| NULL   | cpp    |   41 |
+--------+--------+------+

無條件修改（修改整列的值）

語法：UPDATE 表名
   SET 列名1=值1,列名2=值2,···;
輸入語句：

mysql> UPDATE tb_stu
    -> SET number=1, age=18;

運行結果：

Query OK, 4 rows affected (0.00 sec)
Rows matched: 4  Changed: 4  Warnings: 0

查看錶中各行的值：

+--------+--------+------+
| number | name   | age  |
+--------+--------+------+
| 1      | java   |   18 |
| 1      | c      |   18 |
| 1      | python |   18 |
| 1      | cpp    |   18 |
+--------+--------+------+

有條件修改

語法：UPDATE 表名
   SET 列名1=值1,列名2=值2,···
   WHERE ···;
輸入語句：

mysql> UPDATE tb_stu
    -> SET number=2, age=19
    -> WHERE name='c';

運行結果：

Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

查看錶中各行的值：

+--------+--------+------+
| number | name   | age  |
+--------+--------+------+
| 1      | java   |   18 |
| 2      | c      |   19 |
| 1      | python |   18 |
| 1      | cpp    |   18 |
+--------+--------+------+