# What is the difference between INNER JOIN and OUTER JOIN?

What is the difference between INNER JOIN and OUTER JOIN in SQL?

Assuming you’re joining on columns with no duplicates, which is by far the most 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.

[b]Examples[/b]

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.

[b]inner join[/b]

An inner join using either of the equivalent queries gives the intersection of the two tables, i.e. the two rows they have in common.

select * from a INNER JOIN b on a.a = b.b;
select a.*,b.*  from a,b where a.a = b.b;

a | b
--+--
3 | 3
4 | 4

[b]full outer join[/b]

A full outer join will give you the union of A and B, i.e. All the rows in A and all the rows in B. If something in A doesn't have a corresponding datum in B, then the B portion is null, and vice versa.

select * from a FULL OUTER JOIN b on a.a = b.b;

a    |  b
-----+-----
1  | null
2  | null
3  |    3
4  |    4
null |    6
null |    5``````