MySQL查询以计数表列中重复值的数量
让我们首先创建一个表-
mysql> create table DemoTable( Data int );
使用插入命令在表中插入一些记录-
mysql> insert into DemoTable values(60); mysql> insert into DemoTable values(40); mysql> insert into DemoTable values(50); mysql> insert into DemoTable values(60); mysql> insert into DemoTable values(40); mysql> insert into DemoTable values(80);
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-
+------+ | Data | +------+ | 60 | | 40 | | 50 | | 60 | | 40 | | 80 | +------+ 6 rows in set (0.00 sec)
以下是查询以计算一列中重复值的数量-
mysql> select count(*) from DemoTable group by Data having count(Data) > 1;
这将产生以下输出-
+----------+ | count(*) | +----------+ | 2 | | 2 | +----------+ 2 rows in set (0.03 sec)