Question

我正在使用可在http://www.semwebtech.org/sqlfrontend/

查询的mondial数据库

我试图让所有共享山峰的国家，我尝试了以下查询

select distinct country1.name, country2.name
from (select distinct geo1.country as c1, geo2.country as c2
      from geo_mountain geo1 join
           geo_mountain geo2
           on geo1.mountain = geo2.mountain and
              not(geo1.country = geo2.country)
     ) mountain,
     country country1, country country2
where country1.code = mountain.c1 and country2.code = mountain.c2

问题是我得到的每两个值都是2次，一次是 countryA，countryB ，另一次是 countryB，countryA 我怎样才能摆脱第二对夫妇值已经在结果中了吗？

Answer 1

使用正确的join语法：

select c1.name, c2.name
from (select distinct geo1.country as c1, geo2.country as c2
      from geo_mountain geo1 join
           geo_mountain geo2
           on geo1.mountain = geo2.mountain and
              geo1.country < geo2.country
     ) mountain join
     country c1
     on mountain.c1 = c1.code join
     country c2
     on mountain.c2 = c2.code;

<解决了您的问题。

Answer 2

除了3个国家（如Mousa Ali或Zapaleri）不分享的山脉怎么样？我的意思是，你真的需要两列，还是......？

考虑这样一个问题：

select m.mountain,
  listagg (c.name, ', ') within group (order by c.name) countries
from geo_mountain m, country c
where m.mountain in (select mountain
                     from geo_mountain
                     group by mountain
                     having count(distinct country) > 1
                    )
  and c.code = m.country
group by m.mountain
order by m.mountain;

SQL不同b，一对夫妇，当a，b夫妇已经在结果中

2 个答案: