Database join where

Database

Users

id	lastname	firstname
1	Sardor	Sattarov
2	Nurmuhammad	To’xtayev
3	Jasur	Sattarov

Group_items

id	student_id	group_id
1	2	55
2	1	55
3	2	11

Return example 1

condition

users.id == group_items.student_id do not publish a table that satisfies this desire group_items.id == 55

id	lastname	firstname
3	Jasur	Sattarov

example 2

condition

users.id == group_items.student_id do not publish a table that satisfies this desire group_items.id == 11

id	lastname	firstname
1	Sardor	Sattarov
3	Jasur	Sattarov

Answer

Looks like you want OR instead of AND.

SELECT
    * 
FROM
    users u
    LEFT JOIN group_items gi ON u.id = gi.student_id 
WHERE
    gi.student_id IS NULL 
    OR gi.group_id <> 5

Studends without a group plus studends in all groups but 5.