連接兩個select語句sql

Question

我有兩個希望通過自然連接加入的sql語句，但是由於某些原因，以下內容給了我一個錯誤：

(select city_name
from city
left join country
on country.country_name=city.country_name
where country.continent='Europe'
and city.iscapitol='yes')

natural join

(select city_name
from city
left join country
on country.country_name=city.country_name
where country.continent='Europe'
and city.iscapitol='no';)

我正在使用oracle平台，它拋出的錯誤是：

natural join
*
ERROR at line 7:
ORA-00933: SQL command not properly ended

出現此錯誤的原因是什么？ 任何幫助將不勝感激。

Answer 1

select * from (
(select city_name
from city
left join country
on country.country_name=city.country_name
where country.continent='Europe'
and city.iscapitol='yes')

natural join

(select city_name
from city
left join country
on country.country_name=city.country_name
where country.continent='Europe'
and city.iscapitol='no'))

我已經搬走了; 並添加了外部查詢。 我還建議用明確的join條件替換natural join join

with eurcities as (select city_name, iscapitol, country_name from city
      left join country on country.country_name=city.country_name
      where country.continent='Europe')
select c1.city_name, c2.city_name, c1.country_name 
  from eurcities c1 inner join eurcities c2 on (c1.country_name = c2.country_name) 
  where c1.iscapitol = 'yes' and c2.iscapitol = 'no';

如果沒有with它看起來像：

select c1.city_name, c2.city_name, c1.country_name 
  from (select city_name, iscapitol, country_name from city
            left join country on country.country_name=city.country_name
            where country.continent='Europe') c1 
    inner join (select city_name, iscapitol, country_name from city
            left join country on country.country_name=city.country_name
            where country.continent='Europe') c2 
    on (c1.country_name = c2.country_name) 
  where c1.iscapitol = 'yes' and c2.iscapitol = 'no';

Answer 2

首先，不學習natural join 。 這是一個等待發生的錯誤。 在代碼中不顯示join鍵很危險。 忽略聲明的外鍵關系是不明智的。 依賴命名約定很尷尬。

您可以通過寫這個using 。 因此，修復語法，如下所示：

select *
from (select city_name
      from city left join
           country
           on country.country_name = city.country_name
     where country.continent='Europe' and city.iscapitol = 'yes'
    ) cc join
    (select city_name
     from city left join
          country
          on country.country_name = city.country_name
     where country.continent = 'Europe' and city.iscapitol='no'
    ) cnc
    using (city_name);

請注意，子查詢中的left join s是不必要的。

就是說，我認為聚合是一種更簡單的查詢方法：

      select city_name
      from city join
           country
           on country.country_name = city.country_name
      where country.continent = 'Europe'
      having sum(case when city.iscapitol = 'yes' then 1 else 0 end) > 0 and
             sum(case when city.iscapitol = 'no' then 1 else 0 end) > 0;

或者，如果iscapitol [原文]只需要兩個值，您可以使用此為having條款：

      having min(city.iscapitol) <> max(city.iscapitol)