MySQL多个列有多个COUNT？
您可以将聚合函数SUM()与一起使用IF()。让我们首先创建一个表-
mysql> create table DemoTable ( FirstName varchar(100), LastName varchar(100) );
使用插入命令在表中插入一些记录-
mysql> insert into DemoTable values('Adam','Smith');
mysql> insert into DemoTable values('John','Smith');
mysql> insert into DemoTable values('John','Doe');
mysql> insert into DemoTable values('Bob','Doe');
mysql> insert into DemoTable values('Sam','Smith');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-
+-----------+----------+ | FirstName | LastName | +-----------+----------+ | Adam | Smith | | John | Smith | | John | Doe | | Bob | Doe | | Sam | Smith | +-----------+----------+ 5 rows in set (0.00 sec)
这是对MySQL具有多个列的COUNT个查询。
mysql> select sum(if(FirstName='John',1,0)) as John_Count, sum(if(LastName='Smith',1,0)) as Smith_Count from DemoTable;
这将产生以下输出-
+------------+-------------+ | John_Count | Smith_Count | +------------+-------------+ | 2 | 3 | +------------+-------------+ 1 row in set (0.00 sec)