Select all rows from mysql by id with two columns comparison

Question

I want to select all rows from mysql table by id with two columns comparison, my code:

$q = "SELECT * FROM `users` WHERE (`id` <> `chat.from_id` AND `id` <> `chat.to_id`)";

But when I run it, I get this error:

Message: SQLSTATE[42S22]: Column not found: 1054 Unknown column 'chat.from_id' in 'where clause'
SELECT * FROM `users` WHERE (`id` <> `chat.from_id` AND `id` <> `chat.to_id`)
File: Z:/home/mag.ru/www/panel/gears/db.php
Line: 107
URL: /chat

chat.from_id is present in the chat table. Where is my error?

Answer 1

You don't join the chat table. So you can't use columns from that table in your query. Try

SELECT u.* 
FROM `users` u
LEFT JOIN chat c on u.id = c.from_id or u.id = c.to_id
WHERE c.id is null