如何修復 UNION 語句中的「錯誤 1222 (21000)：使用的 SELECT 語句具有不同的列數」？

SELECT * FROM friends
LEFT JOIN users AS u1 ON users.uid = friends.fid1
LEFT JOIN users AS u2 ON users.uid = friends.fid2
WHERE (friends.fid1 = 1) AND (friends.fid2 > 1)

SELECT fid2 FROM friends
WHERE (friends.fid2 = 1) AND (friends.fid1 < 1)

SELECT friends.*, u.*
FROM friends
JOIN users AS u ON u.uid = friends.fid2
WHERE friends.fid1 = 1 AND friends.fid2 > 1
UNION
SELECT friends.*, u.*
FROM friends
JOIN users AS u ON u.uid = friends.fid1
WHERE friends.fid2 = 1 AND friends.fid1 < 1
ORDER BY RAND()
LIMIT 6;