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MySQL查询为NULL发生设置值

2024-04-25 23:38:06 398

使用ISNULL查找NULL值，并使用MySQLUPDATE和SET更新新值-

update yourTableName
set yourColumnName=yourValue
where yourColumnName IS NULL;

让我们首先创建一个表-

mysql> create table DemoTable768 (
   Clientid int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   ClientName varchar(100),
   ClientAge int
);

使用插入命令在表中插入一些记录-

mysql> insert into DemoTable768(ClientName,ClientAge) values('John',23);
mysql> insert into DemoTable768(ClientName,ClientAge) values(NULL,26);
mysql> insert into DemoTable768(ClientName,ClientAge) values('Carol',28);
mysql> insert into DemoTable768(ClientName,ClientAge) values(NULL,24);

使用select语句显示表中的所有记录-

mysql> select *from DemoTable768;

这将产生以下输出-

+----------+------------+-----------+
| Clientid | ClientName | ClientAge |
+----------+------------+-----------+
|        1 | John       |        23 |
|        2 | NULL       |        26 |
|        3 | Carol      |        28 |
|        4 | NULL       |        24 |
+----------+------------+-----------+
4 rows in set (0.00 sec)

以下是查询以设置NULL出现的值-

mysql> update DemoTable768
   set ClientName='Chris'
    where ClientName IS NULL;
Rows matched: 2 Changed: 2 Warnings: 0

让我们检查视图的描述-

mysql> select *from DemoTable768;

这将产生以下输出-

+----------+------------+-----------+
| Clientid | ClientName | ClientAge |
+----------+------------+-----------+
|        1 | John       |        23 |
|        2 | Chris      |        26 |
|        3 | Carol      |        28 |
|        4 | Chris      |        24 |
+----------+------------+-----------+
4 rows in set (0.00 sec)

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MySQL查询为NULL发生设置值

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