Rsa97

SELECT `u`.*
  FROM `users` AS `u`
  JOIN `user_tags` AS `ut` ON `ut`.`user_id` = `u`.`id`
    AND `ut`.`tag_id` IN (1, 2, ..., N)
  GROUP BY `u`.`id`
  HAVING COUNT(*) = N

SELECT `u`.*
  FROM `users` AS `u`
  JOIN `user_tags` AS `ut` ON `ut`.`user_id` = `u`.`id`
    AND `ut`.`tag_id` IN (1, 2, ..., N)
  GROUP BY `u`.`id`
  HAVING COUNT(DISTINCT `ut`.`tag_id`) = N

CREATE FUNCTION SearchRoot(id INT)
BEGIN
  DECLARE parent INT;
  SET parent = id;
  REPEAT
    SET id = parent;
    SET parent = (SEARCH `id_parent` FROM `table` WHERE `id` = id);
  UNTIL parent > 0 END REPEAT;
  RETURN id;
END

SELECT COUNT(*), 
       SUBSTRING_INDEX(SUBSTRING_INDEX(`params`, '"', -2), '"', 1) AS `type`
  FROM `table`
  GROUP BY `type`