Question

假设我有一个像这样填充的表t：

x y z 
- - - 
A 1 A 
A 4 A 
A 6 B 
A 7 A 
B 1 A 
B 2 A

基本上，列x和z是随机字母和y随机数。

我想按如下方式聚合行：

x z min(y) max(y)
- - ------ ------
A A 1      4
A B 6      6
A A 7      7
B A 1      2

换句话说：假设行按x，y和z排序，请为x和z的每个连续组选择最小和最大y。

请注意，此查询不是我需要的：

select x, z, min(y), max(y)
from t
group by x, z

因为这会导致以下不需要的结果：

x z min(y) max(y)
- - ------ ------
A A 1      7
A B 6      6
B A 1      2

所以问题是：有没有办法在SQL中表达我想要的东西？

（如果解决方案依赖于SQL方言：首选Oracle解决方案。）

Answer 1

这是一个解决方案，但我没有时间一步一步地解释它：

select x, z, min(y), max(y)
from (
  select b.* , sum(switch) over (order by rn) as grp_new 
  from(
    select a.* , 
           case when grp = (lag(grp) over (order by rn))
           then 0 
           else 1 end as switch
    from 
        (select x,y,z, 
                dense_rank() over (order by x, z) as grp,
                row_number() over (order by x, y, z) rn
         from t
    )a
  )b
)c
group by x, z, grp_new
order by grp_new

SQLFIDDLE to test it.

Answer 2

如果您的版本支持WITH和ROW_NUMBER() OVER

，则您未提及Oracle版本

WITH C as
(
select t.*,
       ROW_NUMBER() OVER (order by x,y,z ) as rn
from t
), C2 as 

(
select t1.*,
( 
  select count(*) from c where Rn<=t1.Rn 
                               and (z<>t1.z or x<>t1.x) 
) as Grp
from c t1
) 

select x,z,min(y),max(y) from c2 
group by x,z,grp
order by min(rn)

SQLFiddle demo

Answer 3

试

select x, z, min(y), max(y)
  from (select x, z, y from t order by x, z))
 group by x, z

如何在SQL中聚合有序的行子集？

3 个答案: