如何在MySQL中更新某个字段的特定值（如果为空）？

要更新字段如果它为空，则可以将IS NULL属性与UPDATE命令一起使用。让我们首先创建一个表−

mysql> create table DemoTable
(
   StudentScore int
);
Query OK, 0 rows affected (0.47 sec)

使用插入命令将一些记录插入表中−

mysql> insert into DemoTable values(89);
Query OK, 1 row affected (0.16 sec)
mysql> insert into DemoTable values(NULL);
Query OK, 1 row affected (0.14 sec)
mysql> insert into DemoTable values(45);
Query OK, 1 row affected (0.09 sec)
mysql> insert into DemoTable values(NULL);
Query OK, 1 row affected (0.12 sec)
mysql> insert into DemoTable values(56);
Query OK, 1 row affected (0.14 sec)

使用select语句显示表中的所有记录−

mysql> select *from DemoTable;

这将产生以下输出−

+--------------+
| StudentScore |
+--------------+
|           89 |
|         NULL |
|           45 |
|         NULL |
|           56 |
+--------------+
5 rows in set (0.00 sec)

以下是在MySQL中更新字段如果为空的查询−

mysql> update DemoTable set StudentScore=30 where StudentScore IS NULL;
Query OK, 2 rows affected (0.34 sec)
Rows matched: 2 Changed: 2 Warnings: 0

让我们再次检查表记录。

mysql> select *from DemoTable;

这将产生以下输出−

+--------------+
| StudentScore |
+--------------+
|           89 |
|           30 |
|           45 |
|           30 |
|           56 |
+--------------+
5 rows in set (0.00 sec)

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