使用多個值的內部聯接查詢

Question

我的表結構如下所示：

table:App
|AppID|AppName|AppType|
   1    test     new

table:AppRelease
|AppReleaseID|AppID|ReleaseDate|ReleaseVersion|
   1            1   2012-06-20        2.2
   2            1   2012-06-19        2.3

我寫一個查詢，如下所示：

SELECT A.*,B.ReleaseDate,B.ReleaseVersion 
FROM App as A 
  LEFT JOIN AppRelease as B ON A.AppID=B.AppID

此查詢適用於AppRelease表中的單個值，但AppRelease表中的多個值我想獲取最后添加的值。 有可能在單個查詢中嗎？

Answer 1

SELECT aa.*, bb.AppReleaseID, bb.ReleaseDate
FROM App aa LEFT JOIN (
            SELECT a.AppID, a.AppReleaseID, a.ReleaseDate
            FROM AppRelease a INNER JOIN (
                        SELECT AppID, MAX(ReleaseDate) mx FROM AppRelease 
                        GROUP BY AppID
                    ) b ON a.AppID = b.AppID AND a.ReleaseDate = b.mx
        ) bb ON bb.AppID = aa.AppID

小提琴： http ：//sqlfiddle.com/#！2 / befa2 / 3

Answer 2

要在單個查詢中實現此目的，您需要首先在子查詢中獲取最大值：

SELECT A.*,B.ReleaseDate,B.ReleaseVersion 
FROM App as A 
    LEFT JOIN AppRelease as B ON A.AppID = B.AppI
WHERE B.ReleaseDate = (
    SELECT MAX(ReleaseDate)
    FROM AppRelease
    WHERE AppID = A.AppID GROUP BY AppID
    LIMIT 0, 1
) OR B.ReleaseDate IS NULL;

我認為通過將子查詢用作聯接表還有另一種方法。

Answer 3

我認為使用JOIN最好的方法是從AppRelease中選擇最大值。

SELECT A.*,MAX(B.ReleaseDate),MAX(B.ReleaseVersion)
FROM App as A
LEFT JOIN AppRelease as B ON A.AppID=B.AppID
GROUP BY A.AppID

如果要從語義上獲取最后添加的值，則最好使用子查詢，例如

SELECT A.*,
(SELECT B.ReleaseDate FROM AppRelease as B
WHERE B.AppID=A.AppID ORDER BY B.AppReleaseID DESC LIMIT 1)
as ReleaseDate,
(SELECT B.ReleaseVersion FROM AppRelease as
B WHERE B.AppID=A.AppID ORDER BY B.AppReleaseID DESC LIMIT 1)
as ReleaseVersion
FROM App as A