why does this SQL Code not run?
user_chats
id | user_id | to_user_id | ad_id | timestamp
----------------+---------+------------+---------+-----------
1 | 1 | 6 | 13 | 1513516133
user_messages
id | chat_id | text | user_id | timestamp
----------------+---------+------------+---------+-----------
1 | 1 | Hello | 1 | 1513516133
2 | 1 | Hi! | 6 | 1513516754
I want to get the Chats and order them by user_messages.timestamp. My SQL Code is:
SELECT user_chats.id,
user_chats.timestamp,
ad_id,
title,
user_chats.user_id
FROM user_chats
INNER JOIN ads
ON ads.id = ad_id
WHERE user_chats.user_id = "1"
OR user_chats.to_user_id = "1"
ORDER BY (SELECT id
FROM user_messages
WHERE chat_id = user_chats.id
ORDER BY user_messages.id DESC)