Mysql的合併2數查詢在一個查詢

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個問題，我需要檢查用戶1和用戶2，用戶1必須具有1行&用戶2必須零行Mysql的合併2數查詢在一個查詢

我的問題是：這可能與兩列合併這2個查詢一起

收益爲1行//return 1, 0

來源

2016-05-17 Benjamin W

可以使用sum()用條件來計算的條件有多少次是真的

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

來源

2016-05-17 10:01:53

試試這個：

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

SELECT子句的第一個字段返回user = 1次出現次數，而第二個字段返回user = 2次出現次數。

來源

2016-05-17 10:01:30

是的，這就是所謂的有條件聚集：

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

來源

2016-05-17 10:03:09 sagi

試試這個，

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

來源

2016-05-17 10:04:05 Hytool

爲什麼從表中選擇兩次？這可以在一個選擇中完成。 – sagi

您可以試試這個：

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;

來源

2016-05-17 10:05:17

爲什麼要從表格中選擇兩次？這可以在一個選擇中完成。 – sagi

但是我想用兩張桌子來做。 –

這是一個不必要的計算！ – sagi

你也可以試試這個：

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

來源

2016-05-17 10:17:54

Mysql的合併2數查詢在一個查詢

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