Question

Oracle架构：

tableA
 AA  varchar2   PK       
 BB  number     PK                                    
 CC  varchar2   PK     
 DD  number     PK     
 EE  number

SQL查询：

SELECT
    X1.AA,
    X1.CC,
    X1.DD,
    tableA.EE
FROM
    tableA,
    (SELECT
        AA,
        CC,
        MAX(tableA.DD) DD
    FROM
        tableA
    WHERE
        (tableA.BB = 7 OR tableA.BB = 1)  AND
        tableA.EE <> 1
    GROUP BY
        AA,
        CC
    ORDER BY
        AA ASC,
        CC DESC
    ) X1,
    (SELECT
        AA,
        MAX(tableA.CC) CC
    FROM
        tableA
    WHERE
        (tableA.BB = 7 OR tableA.BB = 1)  AND
        tableA.EE <> 1
    GROUP BY
        AA
    ORDER BY
        AA ASC
    ) X2
WHERE
    X2.AA = X1.AA AND
    X2.CC = X1.CC AND
    X2.AA = tableA.AA AND
    X2.CC = tableA.CC AND
    X1.DD = tableA.DD
ORDER BY
    AA ASC

Answer 1

这是基于YB对查询的解释，该解释非常正常，可能是OP真正想要的。但是，它会过滤输出的行。相反，只需要移动过滤器以计算最大值：

def foo(): Object = ""
val resp: String = foo()

Answer 2

我理解X1和X2表仅用于过滤MAX值。在这种情况下，可以使用窗口函数重写查询：

SELECT AA, CC, DD, EE
FROM (
    SELECT *
         , MAX(CC) OVER (PARTITION BY AA    ) As maxCC
         , MAX(DD) OVER (PARTITION BY AA, CC) As maxDD
    FROM tableA
    WHERE BB In (1, 7) AND EE <> 1
) A
WHERE CC = maxCC AND DD = maxDD;

这将保存几个子查询连接，每个子查询连接都有自己的过滤。

更新：考虑到Gordon Linoff的评论，可以更准确地将其重写为：

SELECT AA, CC, DD, EE
FROM tableA
WHERE (AA, CC, DD) IN (
    SELECT DISTINCT AA
         , MAX(CC) OVER (PARTITION BY AA    ) As CC
         , MAX(DD) OVER (PARTITION BY AA, CC) As DD
    FROM tableA
    WHERE BB In (1, 7) AND EE <> 1
);

如何提高SQL性能？

2 个答案: