Question

SELECT COUNT(*) FROM a WHERE year = 2016 && month = 5 && date = 17 && user = 1
//return 1 row

SELECT COUNT(*) FROM a WHERE year = 2016 && month = 5 && date = 17 && user = 2
//return 0 row

我有2个查询，我需要检查用户1和用户2，用户1必须有1行＆amp;用户2必须为0行

我的问题是：是否可以将这两个查询合并在一起

以2列//return 1, 0

返回1行

Answer 1

您可以使用sum()条件来计算条件为真的次数

SELECT SUM(user = 1) as u1, 
       SUM(user = 2) as u2
FROM a 
WHERE year = 2016 and month = 5 and date = 17

Answer 2

是的，这称为条件聚合：

SELECT count(CASE WHEN `user` = 1 THEN 1 END) as usr1_cnt,
       count(CASE WHEN `user` = 2 THEN 1 END) as usr2_cnt
FROM a
WHERE year = 2016 and month = 5 and date = 17

Answer 3

试试这个：

SELECT SUM(user = 1) AS user1, SUM(user = 2) AS user2
FROM a 
WHERE year = 2016 AND month = 5 AND date = 17

SELECT子句的第一个字段返回user = 1次出现，而第二个字段返回user = 2次出现。

Answer 4

试试这个，

    SELECT
    (
    SELECT COUNT(*) 
    FROM a 
    WHERE year = 2016 && month = 5 && date = 17 && user = 1
    ) AS usr1,
    (
    SELECT COUNT(*) 
    FROM a
     WHERE year = 2016 && month = 5 && date = 17 && user = 2
    ) AS usr2

Answer 5

你也可以尝试这个：

SELECT SUM(user = 1) as user1, 
       SUM(user = 2) as user2
FROM a 
WHERE year = 2016 and month = 5 and date = 17;

Answer 6

你可以试试这个：

SELECT * from (
SELECT COUNT(*) count1 FROM a WHERE year = 2016 && month = 5 && date = 17 &&  user = 1) aa,
(SELECT COUNT(*) count2 FROM a WHERE year = 2016 && month = 5 && date = 17 && user = 2) bb;

Mysql在一个查询中合并2个计数查询

6 个答案: