如何将 WITH 子句与 WHERE 子句结合使用

Question

我有以下查询未运行：

with countf as (
select nationid, count(*) as c from customer
group by nationid
),
maxf as ( select max(nationid) from customer )
select c.customerid, c.nationid from customer c, countf cf, maxf m
where c.nationid = cf.nationid
and cf.c = m

问题似乎是m是记录而不是整数。但是，如果我将其作为子查询运行，如下所示：

cf.c = ( select max(nationid) from customer )

它按预期工作。我认为我使用的是 with 语句，而不是预期的方式。正在尝试

cf.c in maxf

让我假设使用WITH生成的表不应该在WHERE子句中使用。

我知道还有其他方法可以使用all例如获取相同的查询。我真的只对我应该如何使用 with 语句感兴趣。我以后只能用它来SELECT吗？

提前感谢任何形式的帮助。

Answer 1

这是因为条件and cf.c = m应该如下所示

with countf as (
select nationid, count(*) as c from customer
group by nationid
),
maxf as ( select max(nationid) as max_nationid from customer )
select c.customerid, c.nationid from customer c, countf cf, maxf m
where c.nationid = cf.nationid
and cf.c = m.max_nationid

旁注：使用适当的 ANSI 样式JOIN语法，该语法更具可读性，例如

select c.customerid, 
c.nationid from customer c
join  countf cf on c.nationid = cf.nationid
join maxf m on cf.c = m.max_nationid

Answer 2

使用记录语法：

and row(cf.c) = m