如何使這個SQL查詢只有一個SELECT

Question

我只能在一個查詢中創建特定的SQL查詢時遇到問題（我不能兩次訪問數據庫，對於設計體系結構，請相信我）這裏的語句：

我有四個表： 問題， 位置， 國家， 地區

這是他們的一些領域：

Questions 
    id 
    description 
Locations 
    id 
    type (could be 'country' or 'region') 
    question_id 
    country_or_region_id (an id, that holds either the country or the region id) 
Countries 
    id 
    name 
Regions 
    id 
    name 

我想是這樣的：

例子：

1  What is your name?  Venezuela, Colombia    South America 

格式：

question id,  question description,  countries,  regions 

---

編輯：對於那些誰問，我m使用MySQL

編輯：對於那些說這是一個糟糕的設計：我沒有創造它，我不能改變設計，我只需要這樣做，就像現在這樣。

Answer 1

如果這是MySQL的：

SELECT q.ID, 
     q.Description, 
     GROUP_CONCAT(DISTINCT c.name) AS countries, 
     GROUP_CONCAT(DISTINCT r.name) AS regions 
FROM Questions q 
     INNER JOIN Locations l 
      ON l.question_id = q.id 
     LEFT JOIN Countries c 
      ON c.id = country_or_region_id 
      AND l.type = 'country' 
     LEFT JOIN Regions R 
      ON R.id = country_or_region_id 
      AND l.type = 'region' 
GROUP BY q.ID, q.Description; 

如果這是SQL-服務器：

SELECT q.ID, 
     q.Description, 
     countries = STUFF((SELECT ', ' + c.name 
          FROM Locations l 
            INNER JOIN Countries c 
             ON c.id = country_or_region_id 
             AND l.type = 'country' 
          WHERE l.question_id = q.id 
          FOR XML PATH(''), TYPE 
         ).value('.', 'NVARCHAR(MAX)'), 1, 2, ''), 
     regions = STUFF(( SELECT ', ' + r.name 
          FROM Locations l 
            INNER JOIN Regions r 
             ON r.id = country_or_region_id 
             AND l.type = 'region' 
          WHERE l.question_id = q.id 
          FOR XML PATH(''), TYPE 
         ).value('.', 'NVARCHAR(MAX)'), 1, 2, '') 
FROM Questions q; 

Answer 2

取出位置表並添加question_id到區域和國家表

select Q.id, Q.description, C.name as country, R.name as region 
from Questions as Q join Countries as C join Regions as R 
where Q.id = L.question_id and Q.id = C.question_id and Q.id = R.question_id; 

Answer 3

SELECT questions.id 
    , questions.description 
    , Group_Concat(countries.name) As countries 
    , Group_Concat(regions.name) As regions 
FROM questions 
INNER 
    JOIN locations 
    ON locations.question_id = questions.id 
LEFT 
    JOIN countries 
    ON countries.id = locations.country_or_region_id 
    AND locations.type = 'country' 
LEFT 
    JOIN regions 
    ON regions.id = locations.country_or_region_id 
    AND locations.type = 'region' 
GROUP 
    BY questions.id 
    , questions.description