将NULL值设置为0，并使用MySQL SELECT在新列中显示整个列
为此，请使用IFNULL()。让我们首先创建一个表-
mysql> create table DemoTable (Value int);
使用插入命令在表中插入一些记录-
mysql> insert into DemoTable values(NULL); mysql> insert into DemoTable values(10); mysql> insert into DemoTable values(20); mysql> insert into DemoTable values(NULL); mysql> insert into DemoTable values(30);
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-
+-------+ | Value | +-------+ | NULL | | 10 | | 20 | | NULL | | 30 | +-------+ 5 rows in set (0.00 sec)
将NULL值设置为0-
mysql> select Value,IFNULL(Value,0) from DemoTable;
这将产生以下输出-
+-------+-----------------+ | Value | IFNULL(Value,0) | +-------+-----------------+ | NULL | 0 | | 10 | 10 | | 20 | 20 | | NULL | 0 | | 30 | 30 | +-------+-----------------+ 5 rows in set (0.00 sec)