SQL Navigator中的"with ... as"

Question

以下查询有效:

select count(*) from everything where num not in (select num from sometable)

以下查询应该与上面的查询等效,但会导致"无效标识符"错误:

with unwanted as (select num from sometable)
select count(*) from everything where num not in unwanted

第二个查询有什么问题？

Answer 1

语法是这样的:

with unwanted as (select num from sometable)
select count(*) from everything where num not in (select * from unwanted)

显然,只有当select num from sometable部件稍微复杂一些或以后使用过几次时,这才有意义......