仅当MySQL值中具有重复和非重复值的列中仅存在一次时，才从中选择一个值
让我们首先创建一个表-
mysql> create table DemoTable723 (Value int);
使用插入命令在表中插入一些记录-
mysql> insert into DemoTable723 values(100); mysql> insert into DemoTable723 values(200); mysql> insert into DemoTable723 values(200); mysql> insert into DemoTable723 values(100); mysql> insert into DemoTable723 values(300); mysql> insert into DemoTable723 values(400); mysql> insert into DemoTable723 values(400); mysql> insert into DemoTable723 values(600); mysql> insert into DemoTable723 values(400); mysql> insert into DemoTable723 values(200);
使用select语句显示表中的所有记录-
mysql> select *from DemoTable723;
这将产生以下输出-
+-------+ | Value | +-------+ | 100 | | 200 | | 200 | | 100 | | 300 | | 400 | | 400 | | 600 | | 400 | | 200 | +-------+ 10 rows in set (0.00 sec)
以下是从MySQL数据库中选择一个值的查询，前提是该值仅在具有重复和非重复值的列中存在一次-
mysql> select *from DemoTable723 group by Value having count(Value)=1;
这将产生以下输出-
+-------+ | Value | +-------+ | 300 | | 600 | +-------+ 2 rows in set (0.00 sec)