After r82659, the following query was created
SELECT user_name,MAX(user_id) AS user_id,MAX(user_editcount) AS edits,COUNT(ug_group) AS numgroups,MAX(ug_group) AS singlegroup,MIN(user_registration) AS creation,MAX(ipb_deleted) AS ipb_deleted FROM mw_user LEFT JOIN mw_user_groups ON ((user_id=ug_user)) LEFT JOIN mw_ipblocks ON ((user_id=ipb_user AND ipb_deleted=1 AND ipb_auto=0)) FORCE INDEX (user_name) WHERE (ipb_deleted IS NULL) GROUP BY user_name ORDER BY user_name LIMIT 51\G
It needs to be
SELECT user_name,MAX(user_id) AS user_id,MAX(user_editcount) AS edits,COUNT(ug_group) AS numgroups,MAX(ug_group) AS singlegroup,MIN(user_registration) AS creation,MAX(ipb_deleted) AS ipb_deleted FROM mw_user FORCE INDEX (user_name) LEFT JOIN mw_user_groups ON ((user_id=ug_user)) LEFT JOIN mw_ipblocks ON ((user_id=ipb_user AND ipb_deleted=1 AND ipb_auto=0)) WHERE (ipb_deleted IS NULL) GROUP BY user_name ORDER BY user_name LIMIT 51\G
^ It seems in 1.17 (I broke the index inclusion in r79699) it's done a bit hackily...
Version: 1.18.x
Severity: normal