SQL Server: What is the difference between CROSS JOIN and FULL OUTER JOIN?

Question

What is the difference between CROSS JOIN and FULL OUTER JOIN in SQL Server?

Are they the same, or not? Please explain. When would one use either of these?

Answer 1

Here is an example where both the FULL OUTER JOIN and CROSS JOIN return the same result set without NULL returned. Please note the 1 = 1 in the ON clause for the FULL OUTER JOIN:

declare @table1 table (     col1    int,    col2    int ) 
declare @table2 table (     col1    int,    col2    int )

insert into @table1 select  1, 11   union all select    2, 22   

insert into @table2 select  10, 101 union all select     2, 202

select  *
from    @table1 t1 full outer join @table2 t2
    on  1 = 1

(2 row(s) affected)

(2 row(s) affected)
col1        col2        col1        col2
----------- ----------- ----------- -----------
1           11          10          101
2           22          10          101
1           11          2           202
2           22          2           202

select  *
from    @table1 t1 cross join @table2 t2

col1        col2        col1        col2
----------- ----------- ----------- -----------
1           11          10          101
2           22          10          101
1           11          2           202
2           22          2           202

(4 row(s) affected)