SQL查找匹配 - 合并查询

Question

我有三个单独的查询，我想如果可能的合并成一个单一的查询。目的是找到存在于三个表中任何两个中的用户。它们必须至少存在于三张桌子中的两张桌子上。

user (user table) 
user_job_ft_job (full time job) 
user_job_own_venture (startup/own venture) 
user_job_not_looking (not seeking employment) 

-- not seeking and full time 
SELECT * from user_job_not_looking ujnl, user_job_ft_job uj, [user] u 
WHERE 1=1 
AND ujnl.user_id = u.user_id 
AND uj.user_id = u.user_id  

-- own venture and full time 
SELECT * from user_job_own_venture ujov, user_job_ft_job uj, [user] u 
WHERE 1=1 
AND ujov.user_id = u.user_id 
AND uj.user_id = u.user_id 

-- own venture and not looking 
SELECT * from user_job_own_venture ujov, user_job_not_looking ujnl, [user] u 
WHERE 1=1 
AND ujov.user_id = u.user_id 
AND ujnl.user_id = u.user_id 

我想这些查询某种方式合并成一个大的查询，这样我可以更轻松地编写动态代码来处理这一商业案例。

的表的结构并不重要，比知道它们都具有称为USER_ID外键它是[用户]表的主键等。

Answer 1

左外连接会导致查询尝试加入桌子上，但不要求孩子表有一个匹配的记录。如果没有匹配的记录，从该表中的字段将是空。这个查询应该做你需要的。

select * from [user] u 
left outer join user_job_not_looking as ujnl on ujnl.user_id=u.user_id 
left outer join user_job_own_venture as ujov on ujov.user_id=u.user_id 
left outer join user_job_ft_job as uj on uj.user_id=user_id 
where 
(ujnl.user_id is not null and ujov.user_id is not null) or 
(ujnl.user_id is not null and uj.user_id is not null) or 
(ujov.user_id is not null and uj.user_id is not null) 

Answer 2

如果你不想重组，尝试这样的查询：

SELECT 
    * 
FROM 
    user 
    FULL JOIN user_job_not_looking AS ujnl ON ujnl.user_id = user.user_id 
    FULL JOIN user_job_own_venture AS ujov ON ujov.user_id = user.user_id 
    FULL JOIN user_job_ft_job AS ujfj ON ujfj.user_id = user.user_id 
WHERE 
    (ujnl.user_id IS NOT NULL AND ujov.user_id IS NOT NULL) OR 
    (ujnl.user_id IS NOT NULL AND ujfj.user_id IS NOT NULL) OR 
    (ujov.user_id IS NOT NULL AND ujfj.user_id IS NOT NULL)