MySQL CASE语句将自定义值放置为NULL
让我们首先创建一个表-
mysql> create table DemoTable ( FirstName varchar(20) );
使用插入命令在表中插入一些记录-
mysql> insert into DemoTable values('John');
mysql> insert into DemoTable values(NULL);
mysql> insert into DemoTable values('Adam');
mysql> insert into DemoTable values(NULL);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-
+-----------+ | FirstName | +-----------+ | John | | NULL | | Adam | | NULL | +-----------+ 4 rows in set (0.00 sec)
现在让我们使用CASE语句-
mysql> select case when FirstName is NULL then 'UNKNOWN NAME' else FirstName end AS FirstName from DemoTable;
这将产生以下输出-
+--------------+ | FirstName | +--------------+ | John | | UNKNOWN NAME | | Adam | | UNKNOWN NAME | +--------------+ 4 rows in set (0.00 sec)
我们还可以使用IFNULL()-获得相同的结果
mysql> select IFNULL(FirstName,'UNKNOWN NAME') AS FirstName from DemoTable;
这将产生以下输出-
+--------------+ | FirstName | +--------------+ | John | | UNKNOWN NAME | | Adam | | UNKNOWN NAME | +--------------+ 4 rows in set (0.00 sec)
热门推荐
10 诗词送行祝福语大全简短
11 新房开工吉日祝福语简短
12 50多岁生日简短祝福语
13 安徽疫情祝福语简短英语
14 农民朋友发财祝福语简短
15 对生活祝福语简短精辟
16 搬家词简短祝福语朋友
17 女神结婚快乐祝福语简短
18 文学短句祝福语大全简短