3現場SUMS，但只有當有價值

Question

這可能是一個沒有道理的。我有表

遊戲：

guid(PK), puid, gScoreA, gTimesPlayed, gScoreB. 

球員：

puid(PK), pFname, pLname 

我想：

Select 
    player.puid, 
    (SUM(game.gScoreA)/SUM(game.gTimesPlayed)) as skillA, 
    (SUM(game.gScoreB)/SUM(game.gTimesPlayed)) as skillB 
FROM 
    player, 
    game 
WHERE 
    player.puid = game.puid 
ORDER BY 
    skillA DESC, 
    skillB DESC 

所以每場比賽的球員可以有兩種gScoreA或gScoreB始終一個gTimesPlayed。所以，我想所有的SUM(game.gScoreA)僅SUM(game.gTimesPlayed)其中game.gScoreA具有價值和game.gScoreB不和SUM(game.gScoreB)/SUM(game.gTimesPlayed) WHERE gScoreA沒有價值，反之亦然分 - 作爲一個整體在從我的耳朵玩家數據庫...煙霧和蒸汽每個玩家！

Answer 1

SELECT 
    player.puid, 
    SUM(game.gScoreA)/SUM(IF(game.gScoreA IS NOT NULL, game.gTimesPlayed, 0)) as skillA, 
    SUM(game.gScoreB)/SUM(IF(game.gScoreB IS NOT NULL, game.gTimesPlayed, 0)) as skillB 
FROM player INNER JOIN game ON player.puid = game.puid 
GROUP BY player.puid 
ORDER BY 
    skillA DESC, 
    skillB DESC 

使用GROUP BY可以得到每個玩家的結果。

此外，使用JOIN語法而不是逗號式聯接。