How to group MYSQL output separated by comma by column?

Question

MySQL

Good day!
There is the following request:

SELECT 
    `a`.`id` AS  `projectId`,
    `a`.`url` AS `projectUrl`,
    `b`.`user` AS `access_users`
FROM `sites` AS `a`
LEFT JOIN `personal` AS `b` ON `b`.`project` = `a`.`id`

The result is as follows:

You need to group the data by projectID, so that in the access_users column, there are users who have access separated by commas.
Tried to do like this:

SELECT 
    `a`.`id` AS  `projectId`,
    `a`.`url` AS `projectUrl`,
    GROUP_CONCAT(`b`.`user` SEPARATOR ',') AS `access_users`
FROM `l2_sites` AS `a`
LEFT JOIN `l2_personal` AS `b` ON `b`.`project` = `a`.`id`

But it didn’t work out, all the projects were grouped and moved into one line:

Help me fix it, please

Answer 1

Solved the issue by simply adding GROUP BY `a`.`id`.
sorry for the question