Inner join produces only the set of records that match in both Table A and Table B. Full outer join produces the set of all records in Table A and Table B, with matching records from both sides where available. If there is no match, the missing side will contain null. Left outer join produces a complete set of records from Table A, with the matching records (where available) in Table B. If there is no match, the right side will contain null. http://www.codinghorror.com/blog/2007/10/a-visual-explanation-of-sql-joins.html