I'm working for a university project, and I have the following question: I have 2 tables in a Oracle DB... I need to select those rows from table1, which are not included in table2... But the main problem is that I need to exclude that rows from table2 wich was selected once... For example: Table1 Table2 ResultTable id | Number | Letter id | Number | Letter id | Number | Letter _____________________ _____________________ _____________________ 1 4 S 1 6 G 2 2 P 2 2 P 2 8 B 3 5 B 3 5 B 3 4 S 4 4 S 4 4 S 4 1 A 6 2 P 5 1 A 5 1 H 6 2 P 6 2 X So, how you see it, if one row from Table1 has a "twin" in Table2, they both are excluded. Hope I was explicit enough. Sorry for my bad English. Thanks.