MySQL查詢選擇

Question

我有兩個表：

t1 
____________ 
projectID 
userID 
projectExpiration 

t2 
____________ 
usrID 
subscriptioID 
subscriptionExpiration 

我需要選擇從T1，項目ID，其中滿足以下條件：

t1.projectExpiration = older then 3 months 
t2.subscriptioID = '5' 
t2.expiration = older then 3 months 

用戶可以具有其他預訂在T2。我只需要他們在那裏擁有的「5」

我需要幫助把他們放在一起的ID單一訂閱條目的結果。

這裏是我到目前爲止有：

SELECT projectID 
FROM t1 
LEFT JOIN t2 ON (t1.userID = t2.userID) 
WHERE t1.projectExpiration < (CURDATE() - INTERVAL 3 MONTH) 
    AND t2.subscriptionExpiration = 5 
     AND t2.subscriptionExpiration < (CURDATE() - INTERVAL 3 MONTH) 

覺得我卡住了...

Answer 1

你想要一個not exists檢查，以確保5是唯一的行：

select 
    * 
from 
    t1 x 
    inner join t2 y on 
     x.userid = y.userid 
where 
    x.projectexpiration < curdate() - interval 3 month 
    and y.subscriptionid = 5 
    and not exists (
     select 
      1 
     from 
      t2 z 
     where 
      z.userid = x.userid 
      and z.subscriptionid <> 5 
    ) 

我還要提到的是我代替left join這裏使用的inner join。這是因爲你不想搶行，其中一個t2行不存在（你沒有，否則你where條款佔nulls）。所以，這只是無用的開銷。一個inner join讓我們以更清晰的方式得到你想要的結果集。

Answer 2

SELECT 
    sq1.projectID 
FROM 
    (SELECT * FROM T2 WHERE subscriptioID=5 
    AND subscriptionExpiration < DATE(now() - INTERVAL 3 MONTH)) sq2 
    INNER JOIN 
    (SELECT * FROM T1 WHERE projectExpiration < DATE(now() - INTERVAL 3 MONTH)) sq1 
    ON sq12.usrID=sq1=userID 
; 

或

SELECT 
    sq1.projectID 
FROM 
    (SELECT usrID userID,subscriptioID,subscriptionExpiration 
    FROM T2 WHERE subscriptioID=5 
    AND subscriptionExpiration < DATE(now() - INTERVAL 3 MONTH)) sq2 
    INNER JOIN 
    (SELECT * FROM T1 WHERE projectExpiration < DATE(now() - INTERVAL 3 MONTH)) sq1 
    USING (userID) 
; 

或

SELECT 
    sq1.projectID 
FROM 
    (SELECT * FROM T2 WHERE subscriptioID=5 
    AND subscriptionExpiration < DATE(now() - INTERVAL 3 MONTH)) sq2 
    INNER JOIN 
    (SELECT projectID,userID usrID,projectExpiration   
    FROM T1 WHERE projectExpiration < DATE(now() - INTERVAL 3 MONTH)) sq1 
    USING (usrID) 
;