按列A分组但比较B列

Question

这个让我在最后几个小时难过,在这个阶段我觉得我需要一些帮助......

我需要比较单个表中的多个组,并确定col B中列出的项目匹配的位置.例如: -

Col A...............Col B
John................Apple
John................Orange
John................Banana
Mary................Orange
Mary................Strawberry
David...............Apple
David...............Orange
David...............Banana

我希望'John'和'David'返回,因为他们在col B中的项目匹配.希望这是有道理的!提前致谢!G

Answer 1

这是这个解决方案的SQL小提琴,所以你可以自己玩它.

 select A.ColA Person1, B.ColA Person2
    from (select ColA, count(ColB) CountBs
          from tbl
          group by ColA) G1
    join (select ColA, count(ColB) CountBs
          from tbl
          group by ColA) G2 on G1.ColA < G2.ColA
                           and G1.CountBs = G2.CountBs
    join tbl A on A.ColA = G1.ColA
    join tbl B on B.ColA = G2.ColA and A.ColB = B.ColB
group by A.ColA, B.ColA, G1.CountBs
having count(distinct A.ColB) = G1.CountBs

-- subqueries G1 and G2 are the same and count the expected colB's per colA
-- G1 and G2 are joined together to get the candidate matches
--    of ColA with the same number of ColB's
-- we then use G1 and G2 to join into tbl, and further join
--    between A and B where the ColB's match
-- finally, we count the matches between A and B and make sure the counts match
--    the expected count of B's for the pairing