计算MySQL中不同值的数量？
让我们首先创建一个表-
mysql> create table DemoTable -> ( -> Name varchar(100), -> Code varchar(100) -> );
使用插入命令在表中插入一些记录-
mysql> insert into DemoTable values('Chris','0001');
mysql> insert into DemoTable values('Robert','0002');
mysql> insert into DemoTable values('Robert','0003');
mysql> insert into DemoTable values('Chris','0001');使用select语句显示表中的所有记录-
mysql> select *from DemoTable;
输出结果
+--------+------+ | Name | Code | +--------+------+ | Chris | 0001 | | Robert | 0002 | | Robert | 0003 | | Chris | 0001 | +--------+------+ 4 rows in set (0.00 sec)
以下是查询以计算不同值的数量-
mysql> select Name,count(distinct Code) from DemoTable group by Name;
输出结果
+--------+----------------------+ | Name | count(distinct Code) | +--------+----------------------+ | Chris | 1 | | Robert | 2 | +--------+----------------------+ 2 rows in set (0.06 sec)