是否可以比较SQL查询的`WHERE`子句中的*元组*？

是否可以在SQL查询的WHERE子句中比较元组(thanks,a_horse_with_no_name)？那样,我可以转换这个：

/* This is actually a sub-sub-sub-query in the middle *
 * of an incredibly complex stored procedure.         */
SELECT ISNULL(SUM(DT.DetailField),0)
FROM   DetailTable DT
WHERE  DT.ForeignKey = ...
AND    EXISTS (/* I know this sub-sub-sub-sub-query *
                * will return at most one row.      */
               SELECT 'X'
               FROM   HeaderTable HT
               WHERE  HT.HeaderKey    = DT.HeaderKey
               AND    HT.HeaderField1 = ...
               AND    HT.HeaderField2 = ...)

进入类似的东西：

SELECT ISNULL(SUM(DetailField),0)
FROM   DetailTable DT
WHERE  DT.ForeignKey = ...
AND    (SELECT HT.HeaderField1,HT.HeaderField2
        FROM   HeaderTable HT
        WHERE  HT.HeaderKey = DT.HeaderKey) = (...,...)

解决方法

select  *
from    SomeTable t1
outer apply
        (
        select  *
        from    SomeOtherTable t2
        where   t1.Stuff = t2.Unit
        ) sub1
outer apply
        (
        select  *
        from    YetAnotherTable t3
        where   t1.Stuff = t3.jetser
        ) sub2
where   sub1.col1 = sub2.col1
        and sub1.col2 = sub2.col2

（编辑：安卓应用网）

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