wiki.techinc.nl/maintenance/archives/patch-user_groups.sql

--
-- User permissions have been broken out to a separate table;
-- this allows sites with a shared user table to have different
-- permissions assigned to a user in each project.
--
-- This table replaces the old user_rights field which used a
-- comma-separated blob.
--
CREATE TABLE /*$wgDBprefix*/user_groups (
  -- Key to user_id
  ug_user int unsigned NOT NULL default '0',

  -- Group names are short symbolic string keys.
  -- The set of group names is open-ended, though in practice
  -- only some predefined ones are likely to be used.
  --
  -- At runtime $wgGroupPermissions will associate group keys
  -- with particular permissions. A user will have the combined
  -- permissions of any group they're explicitly in, plus
  -- the implicit '*' and 'user' groups.
  ug_group varbinary(16) NOT NULL default '',

  PRIMARY KEY (ug_user,ug_group),
  KEY (ug_group)
) /*$wgDBTableOptions*/;