如何一起選擇與WHERE子句

Question

我有未運行下面的查詢使用WITH子句：

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 

這個問題似乎是m是一個記錄，而不是一個整數。但是，如果我將它作爲子查詢運行如下：

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

它按預期工作。我認爲我正在使用with語句而不是預期的方式。試圖

cf.c in maxf 

讓我假設使用WITH只是不應該在一個WHERE子句中使用生成的表。

我知道還有其他方法可以使用all來獲得相同的查詢。我真的只對我應該如何使用with語句感興趣。我以後只能使用它到SELECT嗎？

在此先感謝您提供任何幫助。

Answer 1

這是因爲條件and cf.c = m這應該是像下面

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 

旁註：使用適當的ANSI風格JOIN語法是更具可讀性像

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

使用記錄語法：

and row(cf.c) = m