MySQL查詢加入

Question

我有一個MySQL問題。它與this other question that I asked previously有關，但略有不同。

我有2個表：團隊，承包商

TEAMS 
|team_id | location| 
-------------------- 
| 1 | space1 | 
-------------------- 
| 2 | space2 | 
-------------------- 
| 3 | space3 | 
-------------------- 
| 4 | space3 | 
-------------------- 

---

CONTRACTORS 
|cont_id | location| team_id| 
----------------------------- 
| 1 | space1 | 1 | 
----------------------------- 
| 2 | space1 | 0 | 
----------------------------- 
| 3 | space3 | 3 | 
----------------------------- 
| 4 | space3 | 3 | 
----------------------------- 
| 5 | space3 | 0 | 
----------------------------- 
| 6 | space3 | 4 | 
----------------------------- 

如果我給出一個TEAM_ID，我想創建一個將找到所有在該位置的承包商查詢給定的team_id並且只屬於給定的team_id或team_id = 0。 （承包商表中的team_id = 0意味着承包商目前不是團隊的一部分）。

例如，我給了team_id = 3.與team_id = 3的團隊位於space3。我想查找位於space3的承包商，僅屬於team_id = 3或team_id = 0（本例中cont_id = 3,4,5）。

有沒有一種方法可以通過單個MySQL查詢來實現這一點？

Answer 1

Select cont_id,team_id,location 
FROM CONTRACTORS 
where team_id = 3 or 
     team_id =0 and 
     location In 
       (
        SElect location 
        from TEAMS 
        where team_id=3 
       ) 

Working Fiddle

輸出：

隨着加入你可以做這樣

SELECT C.cont_id ,C.team_id,T.location 
FROM TEAMS T 
LEFT JOIN CONTRACTORS C 
ON T.location = C.location 
AND (T.team_id = C.team_id OR C.team_id = 0) 
where T.team_id= 3 

Working Fiddle

輸出：

Answer 2

嘗試像這樣

SELECT C.cont_id ,T.team_id,T.locations 
FROM TEAM T 
LEFT JOIN CONTRACTORS C ON T.team_id = C.team_id OR C.team_id = 0 
WHERE T.team_id = 3 

Answer 3

試試這個：

select cont_id, c.team_id, c.location 
from CONTRACTORS c join TEAM t 
on c.team_id = t.team_id 
where c.team_id = GIVEN_TEAM_ID or c.team_id = 0 

Answer 4

替代避免子查詢： -

SELECT C.cont_id ,T.team_id,T.location 
FROM TEAMS T 
LEFT JOIN CONTRACTORS C 
ON T.location = C.location 
AND (T.team_id = C.team_id OR C.team_id = 0) 
WHERE T.team_id = 3 

http://www.sqlfiddle.com/#!2/b9efd/1