Question

我有两个sql语句，我希望通过自然连接加入，但由于某种原因，以下是给我一个错误：

(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，它抛出的错误是：

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

这个错误会出现的原因是什么？任何帮助将不胜感激。

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'))

我已删除;并添加了外部查询。我还建议您使用natural join

的明确条件替换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';

如果没有with，它将如下所示：

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，忘掉natural join。这是一个等待发生的错误。未在代码中显示join键是危险的。忽略声明的外键关系是不明智的。依赖命名约定很尴尬。

您可以使用using来撰写此内容。因此，修复语法，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);

请注意，子查询中的left join是不必要的。

那就是说，我认为聚合是一种更简单的查询方法：

      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 [sic]只接受两个值，则可以将其用于having子句：

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

加入两个select语句sql

2 个答案: