Question

在我的数据库表中，我有两列，其中包含0或1。

我有type和Gender，其中type表示0 => teacher和1 => student，性别表示0 => male和1 => female。

如何编写单个sql查询以获得教师，学生，男性和女性的数量？

现在我有：

select COUNT(type) as teachers from my_table where type = 0; // Teachers
select COUNT(type) as students from my_table where type = 1; // Students
select COUNT(gender) as males from my_table where type = 0; // Males
select COUNT(gender) as females from my_table where type = 1; // Females

可以在一个查询中完成吗？如果是这样，怎么样？

Answer 1

您可以使用CASE功能使用SUM：

SELECT SUM(CASE type WHEN  1 THEN 1 ELSE 0 END) AS students,
       SUM(CASE type WHEN  0 THEN 1 ELSE 0 END) AS teachers,
       SUM(CASE gender WHEN 1 THEN 1 ELSE 0 END) AS females,
       SUM(CASE gender WHEN 0 THEN 1 ELSE 0 END) AS males
FROM my_table;

您也可以使用COUNT功能代替SUM，如下所示：

SELECT COUNT(CASE type WHEN  1 THEN 1 ELSE NULL END) AS students,
       COUNT(CASE type WHEN  0 THEN 1 ELSE NULL END) AS teachers,
       COUNT(CASE gender WHEN 1 THEN 1 ELSE NULL END) AS females,
       COUNT(CASE gender WHEN 0 THEN 1 ELSE NULL END) AS males
FROM my_table;

See this SQLFiddle

Answer 2

这样您就可以在单个查询中执行此操作。如果表中只有两种类型的数据，则无需在IN子句中指定WHERE条件：

SELECT SUM(IF(type = 1, 1, 0)) as students,
       SUM(IF(type = 0, 1, 0)) as teachers,
       SUM(IF(gender = 1, 1, 0)) as females,
       SUM(IF(gender = 0, 1, 0)) as males
FROM my_table
WHERE type IN(0,1)
      AND gender IN(0,1);

Answer 3

您可以使用子查询来实现此目的。

SELECT COUNT(type) AS students,
    (SELECT COUNT(type) FROM my_table WHERE type = 0) As teachers,
    (SELECT COUNT(gender) FROM my_table WHERE gender = 1) AS females,
    (SELECT COUNT(gender) FROM my_table WHERE gender = 0) AS males
FROM my_table WHERE type = 1;

Answer 4

是的，你可以。您是否尝试过将每个SQL语句放在一起？ SQL1 as fld1, SQL2 as fld2, someOtherFieldsIfNeeded FROM ...

MYSQL计数功能合并

4 个答案: