使用 CASE 表达式透视数据

Question

I have the following query which gets the store, the week number and the sum of products sold:

select *
from 
(
  select store, week, xCount
  from yt
) src
pivot
(
  sum(xcount)
  for week in ([1], [2], [3])
) piv;

Is it possible to get the same result with CASE expression?

Answer 1

You can pivot with conditional aggregation as follows:

select 
    store, 
    sum(case when week = 1 then xcount else 0 end) week1,
    sum(case when week = 2 then xcount else 0 end) week2,
    sum(case when week = 3 then xcount else 0 end) week3
from yt
group by store

I tend to prefer conditional aggregation over database-specific pivot syntaxes:

• conditional aggregation is more flexible than pivot

• the syntax works across most databases, so it is much more portable

• performance is usually equivalent