Pernyataan pertama dalam UNION mengembalikan empat kolom:
SELECT b.id AS id,
b.pid AS pid,
b.message AS message,
b.date AS date
FROM wall_posts AS b
Yang kedua mengembalikan enam , karena * diperluas untuk menyertakan semua kolom dari WALL_POSTS
:
SELECT b.id,
b.date,
b.privacy,
b.pid.
b.uid message
FROM wall_posts AS b
UNION
dan UNION ALL
operator mengharuskan:
- Jumlah kolom yang sama ada di semua pernyataan yang membentuk kueri UNION
- Tipe data harus cocok di setiap posisi/kolom
Gunakan:
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))