ALTER TABLE core_group_member ADD COLUMN user_id int(11) NOT NULL default 0;
+
+-- remove duplicates...
+delete from core_group_member where id in (
+ select mid FROM (
+ select
+ concat(group_id,'-',user_id) as uid,
+ max(id) as mid,
+ count(*) as n
+ from
+ core_group_member
+ group by
+ group_id,user_id
+ having n > 1
+ ) s
+)
+
+
ALTER TABLE core_group_member ADD UNIQUE KEY unique_group_user (group_id,user_id);