UNION中的第一条语句返回四列：
SELECT b.id AS id,
b.pid AS pid,
b.message AS message,
b.date AS date
FROM wall_posts AS b
第二个返回 ，因为*扩展为包括以下所有列WALL_POSTS：
SELECT b.id,
b.date,
b.privacy,
b.pid.
b.uid message
FROM wall_posts AS b
在UNION与UNION ALL运营商要求：
使用：
FROM ((SELECT b.id AS id,
b.pid AS pid,
b.message AS message,
b.date AS date
FROM wall_posts AS b
JOIN Friends AS f ON f.id = b.pid
WHERE f.buddy_id = '1' AND f.status = 'b'
ORDER BY date DESC
LIMIT 0, 10)
UNION
(SELECT id,
pid,
message,
date
FROM wall_posts
WHERE pid = '1'
ORDER BY date DESC
LIMIT 0, 10))
602392714
清零编程群