Question

这是一张桌子

   A    B   C   D   R
  'a'   1   3   1   0
  'a'   2   3   1   1
  'a'   2   3   1   0
  'b'   1   3   1   1
  'b'   2   4   3   2
  'b'   1   4   3   0
  'c'   2   4   3   0

R与A的交叉表如下：

     A  R   count

     a  0   2
     a  1   1
     a  2   0
     b  0   1
     b  1   1
     b  2   1
     c  0   1
     c  1   0
     c  2   0

交叉制表给出了R的频率取决于A。

此操作的sql查询是什么？

Answer 1

我会使用CROSS JOIN和LEFT JOIN

select ta.a, tr.r, count(t.a) 
from (select distinct a from tab) TA
cross join (select distinct r from tab) TR
left join tab t on t.a = ta.a and t.r = tr.r
group by ta.a, tr.r

Answer 2

使用CROSS JOIN和条件总和来实现计数：

  declare @Table table (A char(1), B int, C int, D int, R int)
  Insert into @Table values
   ('a', 1, 3, 1, 0)
  , ('a', 2, 3, 1, 1)
  , ('a', 2, 3, 1, 0)
  , ('b', 1, 3, 1, 1)
  , ('b', 2, 4, 3, 2)
  , ('b', 1, 4, 3, 0)
  , ('c', 2, 4, 3, 0)

  select A, x.R, Sum(iif(x.r = t.R, 1, 0))
  from @Table t
  cross join (Select distinct R from @Table) x
  group by A, x.R
  order by a, x.R

跨表查询单个任务

2 个答案: