A common example of correlated join criteria would be: select . . . where make='FORD' and model='MUSTANG'; The CBO doesn't know that all Mustangs are built by Ford, so it's not aware that the extra filter condition won't really filter out any more rows. Regards, Brandon -----Original Message----- From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of hrishy I didnt quite understand the statement "Check if the join criteria between SC and SH are correlated" Privileged/Confidential Information may be contained in this message or attachments hereto. Please advise immediately if you or your employer do not consent to Internet email for messages of this kind. Opinions, conclusions and other information in this message that do not relate to the official business of this company shall be understood as neither given nor endorsed by it.