用于获取朋友名称的SQL表达式

Question

我正在使用SQL制作朋友网络功能。我使用了以下代码：

SELECT relationship.requester, 
       relationship.requested, 
       user.firstname, 
       user.lastname 
  FROM relationship 
  JOIN user ON (user.guid = relationship.requester
           OR user.guid = sqrelationship.requested) 
 WHERE relationship.requester = {$userid} 
    OR relationship.requested = {$userid} 
   AND relationship.approved = 1

SQL将返回一个表，其中包含用户发起或接收的已批准关系的ID。但是，user.firstname和user.lastname只返回一组结果。如何使这个表达式能够同时获取请求者和被请求者的名字？

Answer 1

很难说明你没有指定表格设计的问题，但我猜是这样的：

select relationship.requester, relationship.requested, 
       requester.firstname, requester.lastname,
       requested.firstname, requested.lastname,
from relationship
left join user as requester on user.guid = relationship.requester 
left join user as requested on user.guid = relationship.requested
where relationship.requester = {$userid}
  and relationship.approved = 1