They do not. The id columns are all not null columns. The source database this one was refreshed from does not exhibit this behavior. Everything is identical between them - init.ora params, database options, etc. From: Peter Khmelnitsky [mailto:peter.khmelnitsky@xxxxxxxxxxxxxxxx] Sent: Wednesday, October 24, 2012 3:33 PM To: Ramadoss, Karthik Cc: oracle-l@xxxxxxxxxxxxx; oracle-l-bounce@xxxxxxxxxxxxx Subject: Re: SQL question Do these tables have null values in key columns (*.id) From: "Ramadoss, Karthik" <Karthik.Ramadoss@xxxxxxxxxxxxxxxx<mailto:Karthik.Ramadoss@xxxxxxxxxxxxxxxx>> To: "oracle-l@xxxxxxxxxxxxx<mailto:oracle-l@xxxxxxxxxxxxx>" <oracle-l@xxxxxxxxxxxxx<mailto:oracle-l@xxxxxxxxxxxxx>> Date: 10/24/2012 03:03 PM Subject: SQL question Sent by: oracle-l-bounce@xxxxxxxxxxxxx<mailto:oracle-l-bounce@xxxxxxxxxxxxx> ________________________________ This is probably a simple one but definitely something new for me. Database: 11.2.0.3 OS: Oracle Linux 5.6 A SQL like SELECT A.COL1, A.COL2, B.COL3 FROM TABLE1 A, TABLE2 B, TABLE3 C WHERE A.ID = B.ID AND B.ID = C.ID returns 1,192,940 rows. And SELECT COUNT(*) from (SELECT A.COL1, A.COL2, B.COL3 FROM TABLE1 A, TABLE2 B, TABLE3 C WHERE A.ID = B.ID AND B.ID = C.ID) Returns 1,192,978 rows. Anyone know what is going on here? I would expect both to return the same number of rows. -- //www.freelists.org/webpage/oracle-l -- //www.freelists.org/webpage/oracle-l