Slow query - correlated or not?

Hi We have an update that is taking a very long time to run. I have turned into a select statement for testing. I have included the set explain output. My questions are: Is this a correlated subquery? ie is the full table scan of ps_jrnl_ln occurring for each row being updated? Does this explain why ps_jrnl_ln does not appear in the subquery section of sqexplain.out? Any ideas on improving performance would be much appreciated. Thanks William QUERY: ------ select count(*) from'psoft'.PS_JRNL_LN WHERE BUSINESS_UNIT='UOA' AND EXISTS (SELECT 'X' FROM 'psoft'.PS_COMBO_DATA_TBL WHERE SETID='UOFAK' AND PROCESS_GROUP='INCSTMT' AND VALID_CODE='V' AND 'psoft'.PS_JRNL_LN.JOURNAL_DATE BETWEEN EFFDT_FROM AND EFFDT_TO AND 'psoft'.PS_JRNL_LN.ACCOUNT = ACCOUNT AND 'psoft'.PS_JRNL_LN.DEPTID = DEPTID) Estimated Cost: 1614158848 Estimated # of Rows Returned: 1 1) psoft.ps_jrnl_ln: SEQUENTIAL SCAN Filters: (psoft.ps_jrnl_ln.business_unit = 'UOA' AND EXISTS <subquery> ) Subquery: --------- Estimated Cost: 1200 Estimated # of Rows Returned: 1 1) psoft.ps_combo_data_tbl: INDEX PATH Filters: (psoft.ps_combo_data_tbl.valid_code = 'V' AND (psoft.ps_combo_data_tbl.effdt_from <= psoft.ps_jrnl_ln.journal_date AND (psoft.ps_combo_data_tbl.effdt_to >= psoft.ps_jrnl_ln.journal_date AND (psoft.ps_combo_data_tbl.account = psoft.ps_jrnl_ln.account AND psoft.ps_combo_data_tbl.deptid = psoft.ps_jrnl_ln.deptid ) ) ) ) (1) Index Keys: setid process_group combination valid_code (Serial, fragments: ALL) Lower Index Filter: (psoft.ps_combo_data_tbl.setid = 'UOFAK' AND psoft.ps_combo_data_tbl.process_group = 'INCSTMT' )