MySQL的两个表

Question

选择我有两个表中的字段的巫帮[仅需提到]

- partners 
    - id [PRI, int] 
    - name [varchar(20)] 
    - match [=matches.id] 
    - can_call [int] 


- players 
    - registered [0/1] 
    - partner [=partners.id] 
    - match [=matches.id] 

现在，我需要一个查询，这将使一个int - 有多少球员能的合作伙伴之一调用;

要获得多少玩家所要求的任何比赛的任何搭档，我使用：

SELECT COUNT(id) 
FROM players 
WHERE registered=1 
    AND partner=PARTNER_ID 
    AND match=MATCH_ID 

现在，我需要有这样的事情：

SELECT (can_call-THE_ABOVE) as free 
FROM partners 
WHERE match=MATCH_ID 

而且我不知道如何做到这一点:)

的理念是：获得免费的位置，因为我们想为我们想要的比赛的合作伙伴，然后选择。减去COUNT（ID）的球员，已经被注册了那场比赛由合作伙伴。

谢谢！ [我希望我有道理^ _ ^]

编辑：我已经解决了（在两个加入答案之前）。我可能会用我的解决方案，因为它更简单;但我会看起来更到其他的答案，一旦我会想成为MySQL的用户advnaced，谢谢大家^^

Answer 1

没关系，理解了它;它是完全按照我上面的伪代码：

SELECT can_call - (SELECT COUNT(id) FROM players WHERE ...) as free 
    WHERE match=MATCH_ID AND id=PARTNER_ID 

^^

Answer 2

Select P.name 
    , P.can_call - Coalesce(Calls.CallCount,0) As CanCall 
From partners As P 
    Left Join (
       Select partner, match, Count(*) As CallCount 
       From players As P1 
       Where registered = 1 
       Group By partner, match, 
       ) As Calls 
     On Calls.partner = P.id 
      And Calls.match = P.match 
Where P.match = MATCH_ID 

Answer 3

SELECT pa.can_call-COUNT(pl.id) 
     AS free 
FROM partners pa 
    LEFT JOIN players pl 
    ON pl.registered=1 
     AND pl.partner=pa.id 
     AND pl.match=pa.match 
WHERE pa.id=PARTNER_ID 
    AND pa.match=MATCH_ID 
GROUP BY pa.id 
     , pa.match