Форуми / Craftwork / Server-side / merge the data base...

What you need to do is this:

INSERT IGNORE INTO `sed_groups_users` (`gru_userid`, `gru_groupid`)
    SELECT `user_id`, `user_maingrp` FROM `sed_users`;

This will add the main groups into sed_groups_users. After that you'll have to add secondary groups manually for each user.