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MySQL更新列为NULL的空白值

2024-04-26 01:27:05 432

为此，可以IF()与UPDATE命令一起使用。让我们首先创建一个表-

mysql> create table DemoTable1601
   -> (
   -> FirstName varchar(20) ,
   -> LastName varchar(20)
   -> );

使用插入命令在表中插入一些记录-

mysql> insert into DemoTable1601 values('John','Doe');
mysql> insert into DemoTable1601 values('Adam','');
mysql> insert into DemoTable1601 values('David','Miller');
mysql> insert into DemoTable1601 values('Chris','');

使用select语句显示表中的所有记录-

mysql> select * from DemoTable1601;

这将产生以下输出-

+-----------+----------+
| FirstName | LastName |
+-----------+----------+
| John      |      Doe |
| Adam      |          |
| David     |   Miller |
| Chris     |          |
+-----------+----------+
4 rows in set (0.00 sec)

以下是将列更新为null或其值的查询-

mysql> update DemoTable1601 set LastName=if(LastName='',NULL,LastName);
Rows matched: 4  Changed: 2 Warnings: 0

让我们再次检查表记录-

mysql> select * from DemoTable1601;

这将产生以下输出-

+-----------+----------+
| FirstName | LastName |
+-----------+----------+
| John      |      Doe |
| Adam      |     NULL |
| David     |   Miller |
| Chris     |     NULL |
+-----------+----------+
4 rows in set (0.00 sec)

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MySQL更新列为NULL的空白值

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