Hi, better is walk throught tree
------------------------------------------------------------------ WITH RECURSIVE R_TREE AS ( SELECT TT.ID, TT.ID AS TOP_PARENT FROM TABLE1 TT WHERE TT.PARENT_ID IS NULL UNION ALL SELECT TT.ID, RT.TOP_PARENT FROM TABLE1 TT JOIN R_TREE RT ON RT.ID = TT.PARENT_ID ) SELECT RT2.ID, CASE WHEN RT2.ID=RT2.TOP_PARENT THEN NULL ELSE RT2.TOP_PARENT END AS TOP_PARENT FROM R_TREE RT2 ------------------------------------------------------------------ the result plan show obvious difference above query PLAN (R_TREE TT NATURAL, R_TREE TT NATURAL) instead PLAN (R NATURAL, HASH (TREE ROOT NATURAL, TREE T NATURAL), TREE M NATURAL) ------------------------------------------------------------------ and with indexes ------------------------------------------------------------------ above query PLAN (R_TREE TT INDEX (IXA_TABLE1__PARENT_ID), R_TREE TT INDEX (IXA_TABLE1__PARENT_ID)) instead previus PLAN (R INDEX (IXA_TABLE1__PARENT_ID), JOIN (TREE ROOT INDEX (IXA_TABLE1__PARENT_ID), TREE T INDEX (IXA_TABLE1__PARENT_ID)), TREE M INDEX (IXA_TABLE1__PARENT_ID)) Regards, Karol Bieniaszewski ------------------------------------ ------------------------------------ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Visit http://www.firebirdsql.org and click the Documentation item on the main (top) menu. Try FAQ and other links from the left-side menu there. Also search the knowledgebases at http://www.ibphoenix.com/resources/documents/ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ ------------------------------------ Yahoo Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/firebird-support/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/firebird-support/join (Yahoo! ID required) <*> To change settings via email: firebird-support-dig...@yahoogroups.com firebird-support-fullfeatu...@yahoogroups.com <*> To unsubscribe from this group, send an email to: firebird-support-unsubscr...@yahoogroups.com <*> Your use of Yahoo Groups is subject to: https://info.yahoo.com/legal/us/yahoo/utos/terms/
