如何在此联合结果中添加列？

Question

我有这个查询(我为了简洁而删除了一些键):

SELECT id as in_id, out_id, recipient, sender, read_flag 
  FROM received WHERE recipient=1
UNION ALL 
SELECT in_id, id AS out_id, recipient, sender, read_flag  
  FROM sent WHERE sender=1 

它结合了两个表的结果,显示给定用户发送和接收的消息.我想要做的是在结果中添加一个列/标志以区分该行所属的表,因此当我显示它时,我可以显示已发送或已接收消息的相关图标.我该如何添加？

Answer 1

只需为每个查询添加一个常量列.只要它在两个部分都是相同的,那么类型是什么并不重要.所以你可以使用0和1或两个字符串,例如:

SELECT id as in_id, out_id, recipient, sender, read_flag , 'received' as source
  FROM received WHERE recipient=1
UNION ALL 
SELECT in_id, id AS out_id, recipient, sender, read_flag , 'sent' as source 
  FROM sent WHERE sender=1