Difference between INNER and OUTER joins In a database such as MSSQL, data is divided into a number of tables which are then connected (Joined) together by JOIN in SELECT commands to read records from multiple tables. Assuming you're joining on columns with no duplicates, which is a very common case: An inner join of A and B gives the result of A intersect B, i.e. the inner part of a venn diagram intersection. An outer join of A and B gives the results of A union B, i.e. the outer parts of a venn diagram union. Examples Suppose you have two Tables, with a single column each, and data as follows: A B - - 1 3 2 4 3 5 4 6 Note that (1,2) are unique to A, (3,4) are common, and (5,6) are unique to B. Inner join An inner join using either of the equivalent queries gives the intersection of the two tables, i.e. the tw...