DISTINCT 和 TOP合用，谁先起作用？[@more@]

实验：

IF (OBJECT_ID('tempdb..#tmp_a')) IS NOT NULL
DROP table #tmp_a

CREATE table #tmp_a (a int)

insert into #tmp_a select 1
insert into #tmp_a select 2
insert into #tmp_a select 2
insert into #tmp_a select 2
insert into #tmp_a select 3

select * from #tmp_a

SELECT DISTINCT TOP 3 * from #tmp_a

根据以上结果得知：系统先distinct运算再top运算。

ITPub博客

DISTINCT 和 TOP合用的执行顺序