MySQL查询将空值转换为NULL？
使用SET和WHERE将空值转换为NULL很容易。让我们首先创建一个表-
mysql> create table DemoTable1315 -> ( -> CountryName varchar(10) -> );
使用insert命令在表中插入一些记录。我们也在这里设置了一些空值-
mysql> insert into DemoTable1315 values('US');
mysql> insert into DemoTable1315 values('');
mysql> insert into DemoTable1315 values('UK');
mysql> insert into DemoTable1315 values('');
mysql> insert into DemoTable1315 values('');
mysql> insert into DemoTable1315 values('AUS');使用select语句显示表中的所有记录-
mysql> select *from DemoTable1315;
输出结果
+-------------+ | CountryName | +-------------+ | US | | | | UK | | | | | | AUS | +-------------+ 6 rows in set (0.00 sec)
这是将空值转换为NULL的查询-
mysql> update DemoTable1315 set CountryName=NULL where CountryName=''; Rows matched: 3 Changed: 3 Warnings: 0
让我们再次检查表记录-
mysql> select *from DemoTable1315;
输出结果
+-------------+ | CountryName | +-------------+ | US | | NULL | | UK | | NULL | | NULL | | AUS | +-------------+ 6 rows in set (0.00 sec)