如何在MySQL中为空行设置默认值？
要为空行设置默认值，请使用COALESCE()的概念。让我们首先创建一个表-
create table DemoTable1863
(
FirstName varchar(20)
);使用插入命令在表中插入一些记录-
insert into DemoTable1863 values('Chris');
insert into DemoTable1863 values(NULL);
insert into DemoTable1863 values('David');
insert into DemoTable1863 values(NULL);使用select语句显示表中的所有记录-
select * from DemoTable1863;
这将产生以下输出-
+-----------+ | FirstName | +-----------+ | Chris | | NULL | | David | | NULL | +-----------+ 4 rows in set (0.00 sec)
以下是为空行设置默认值的查询-
select coalesce(FirstName,'UNKNOWN NAME') from DemoTable1863;
这将产生以下输出-
+------------------------------------+ | coalesce(FirstName,'UNKNOWN NAME') | +------------------------------------+ | Chris | | UNKNOWN NAME | | David | | UNKNOWN NAME | +------------------------------------+ 4 rows in set (0.00 sec)