SQL 删除 NULL 并重新组合

Question

我在 table1 上有数据

ClassA  CountA     ClassB    CountB     ClassC   CountC     Catergory
Test1     2        Test2       1          null     null      Group1
null      null     Test3       2          null     null      Group2
null      null      null       null       Test3     3        Group3

我怎样才能重做可以摆脱 NULL 和 bygroup (group1 = test1, group2 = test2, group3 = test3)

ClassA  CountA    Catgroup1   ClassB    CountB  CatGroup2    ClassC   CountC    Catgroup3
Test1     2        Group1      Test2      1       Group2     Test3      2        Group3
                               Test3      3                                      Group3

Answer 1

这是一个真正的痛苦。基本上，您必须独立完成每一列，然后将它们重新组合在一起。

请注意，您不能保留原始顺序，除非您有一列指定顺序。这个想法是为每列中的每个有效值生成一个序列号，并使用full join 将它们重新组合在一起：

select classA.classA, countA.countA, classB.classB, . . . 
from (select classA, row_number() over (order by (select null)) as seqnum
      from t
      where classA is not null
     ) classA full join
     (select countA, row_number() over (order by (select null)) as seqnum
      from t
      where countA is not null
     ) countA
     on classA.seqnum = countA.seqnum full join
     (select classB, row_number() over (order by (select null)) as seqnum
      from t
      where classB is not null
     ) classB
     on classB.seqnum = coalesce(classA.seqnum, countA.seqnum) full join
     . . .
order by seqnum;