MySQL查询显示具有重复记录的列中不同记录的计数
让我们首先创建一个表-
mysql> create table DemoTable ( StudentId int, StudentFirstName varchar(100) );
使用插入命令在表中插入一些记录-
mysql> insert into DemoTable values(100,'John'); mysql> insert into DemoTable values(101,'Chris'); mysql> insert into DemoTable values(102,'John'); mysql> insert into DemoTable values(103,'Sam'); mysql> insert into DemoTable values(104,'Sam');
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-
+-----------+------------------+ | StudentId | StudentFirstName | +-----------+------------------+ | 100 | John | | 101 | Chris | | 102 | John | | 103 | Sam | | 104 | Sam | +-----------+------------------+ 5 rows in set (0.00 sec)
以下是查询以显示具有重复记录的列中不同记录的计数-
mysql> select count(distinct StudentFirstName) from DemoTable;
这将产生以下输出-
+----------------------------------+ | count(distinct StudentFirstName) | +----------------------------------+ | 3 | +----------------------------------+ 1 row in set (0.00 sec)