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MySQL多个列有多个COUNT？

2024-05-15 18:11:40 364

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)

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MySQL多个列有多个COUNT？

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