[sql] full outer join vs cross join

source: http://social.msdn.microsoft.com/Forums/sqlserver/en-US/2412fe92-7ea6-4de2-9599-c0075f246e23/cross-join-vs-full-outer-join?forum=transactsql

Full outer join returns all matching rows from A and B and all Rows from A that are not in B and all rows from B that are not in A.

example:

A

1
2
3

B
2
3
4

select * from A full join B on A.id = B.ID
Output

A  B
1 NULL
2  2
3  3
NULL 4

In a cross join you will get 9 rows combined with each other:

select * from A cross join B
A B
1 4
2 4
3 4
1 2
2 2
3 2
1 3
2 3
3 3

Note: 

However, if a WHERE clause is added, the cross join behaves as an inner join. For example, the following Transact-SQL queries produce the same result set.

(source: http://studentboxoffice.in/Articles.aspx?id=46)