Question

SELECT COL1,
    COL2,
    COL3
FROM TABLE1,
    TABLE2,
    TABLE3,
    TABLE4
WHERE TABLE1.KEY1 = TABLE2.KEY1
    AND TABLE2.KEY = TABLE3.KEY
    AND TABLE2.FILTER = 'Y'
    AND TABLE3.FILTER = 'Y'
    AND TABLE2.KEY = TABLE3.KEY
    AND TABLE3.KEY = TABLE4.KEY

我有类似的查询，我需要进行修改，在表3中有一个日期列，我需要选择最高日值行进行加入。假设表3中有4行对连接感到满意，我需要从这4行中选出最高日期行以进行连接，然后显示结果。

希望问题很清楚。数据库oracle 10g

Answer 1

尝试类似此查询的内容。

SELECT
    COL1,
    COL2,
    COL3,
    T33.*

FROM TABLE1

JOIN TABLE2 ON TABLE1.KEY1 = TABLE2.KEY1

JOIN TABLE4 ON TABLE2.KEY = TABLE4.KEY

JOIN

(
    SELECT MAX(T.Day) as DT, T.KEY
    FROM TABLE3 T
    WHERE T.FILTER = 'Y'
    GROUP BY T.KEY
) T3 on TABLE4.KEY = T3.KEY

JOIN TABLE3 T33 ON T3.KEY = T33.KEY AND T3.DT = T33.Day

WHERE

TABLE2.FILTER = 'Y'

主要思想是代替中加入TABLE3即可：

SELECT MAX(T.Day) as DT, T.KEY
FROM TABLE3 T
WHERE T.FILTER = 'Y'
GROUP BY T.KEY

为该表/记录集命名并加入其中。

然后您可以再次加入原始TABLE3（请参阅T33）
从TABLE3中提取所有其他所需的列 T3中没有出现。

我认为你可以解决其他问题。

Answer 2

要最低限度地修改当前查询，您可以在WHERE子句中添加条件

AND TABLE3.DATE = (SELECT MAX(DATE) FROM TABLE3 WHERE TABLE3.FILTER = 'Y')

虽然将来我建议使用显式JOINS。

SELECT COL1,
    COL2,
    COL3
FROM TABLE1 
    INNER JOIN TABLE2 ON TABLE1.KEY1 = TABLE2.KEY1
    INNER JOIN TABLE3 ON TABLE2.KEY = TABLE3.KEY
    INNER JOIN TABLE4 ON TABLE3.KEY = TABLE4.KEY
WHERE 
    TABLE2.FILTER = 'Y'
    AND TABLE3.FILTER = 'Y'
    AND TABLE3.DATE = (SELECT MAX(DATE) FROM TABLE3 WHERE TABLE3.FILTER = 'Y')

从表中加入最大日期

2 个答案: