问题在联盟加入对于MySQL查询

Question

我设法从节省我的最新文章

一个表中选择，但我需要有双重条件在选择

这里是我的代码：

$sql_query = "SELECT b.*,u.username AS MY_Sender 
FROM TABLE_users u,TABLE_blogs b 
Where b.reciever = '0' AND u.user_id = b.sender 
UNION 
SELECT b.*,u.username AS MY_reciever 
FROM TABLE_users u,TABLE_blogs b 
Where b.reciever != '0' AND u.user_id = b.reciever 
ORDER BY bid DESC 
LIMIT 0,7 "; 

但MY_reciever是空的和空的

我在使用UNION这个需要？

Answer 1

SELECT b.*,u.username AS MY_Sender, NULL AS MY_reciever 
FROM TABLE_users u,TABLE_blogs b 
Where b.reciever = '0' AND u.user_id = b.sender 
UNION 
SELECT b.*, NULL AS MY_Sender, u.username AS MY_reciever 
FROM TABLE_users u,TABLE_blogs b 
Where b.reciever != '0' AND u.user_id = b.reciever 

Answer 2

跨工会的各个部分的列必须具有相同的名称。 尝试：

SELECT b.*, 
     u.username AS MY_User 
    FROM TABLE_users u, 
     TABLE_blogs b 
WHERE b.reciever = '0' 
    AND u.user_id = b.sender 
UNION 
SELECT b.*, 
     u.username AS MY_User 
    FROM TABLE_users u, 
     TABLE_blogs b 
WHERE b.reciever != '0' 
    AND u.user_id = b.reciever 
ORDER BY bid DESC 
LIMIT 0,7 

如果您需要区分其中记录已被返回联盟的一部分，返回一个额外的列：

SELECT b.*, 
     u.username AS MY_User. 
     'Sender' AS MyType 
    FROM TABLE_users u, 
     TABLE_blogs b 
WHERE b.reciever = '0' 
    AND u.user_id = b.sender 
UNION 
SELECT b.*, 
     u.username AS MY_User. 
     'Recipient' AS MyType 
    FROM TABLE_users u, 
     TABLE_blogs b 
WHERE b.reciever != '0' 
    AND u.user_id = b.reciever 
ORDER BY bid DESC 
LIMIT 0,7 

Answer 3

@Mac泰勒

嘿，你确定你了解我，告诉你我需要在你写的这个声明中增加一个条件，AS My_Real_Sender ..你可能知道你写的这个声明是f INE找到Reciver（MY_Type），而不是后

的发送者你的意思是这样的吗？

SELECT b.*, 
     u.username AS MY_Sender. 
     NULL as MY_Recipient, 
     'Sender' AS MyType 
    FROM TABLE_users u, 
     TABLE_blogs b 
WHERE b.reciever = '0' 
    AND u.user_id = b.sender 
UNION 
SELECT b.*, 
     u1.username AS MY_Sender. 
     u2.username AS MY_Recipient. 
     'Recipient' AS MyType 
    FROM TABLE_users u1, 
     TABLE_users u2, 
     TABLE_blogs b 
WHERE b.reciever != '0' 
    AND u1.user_id = b.reciever 
    AND u2.user_id = b.sender 
ORDER BY bid DESC 
LIMIT 0,7