What are the uses for Cross Join?
If you have a "grid" that you want to populate completely, like size and color information for a particular article of clothing:
select
size,
color
from
sizes CROSS JOIN colors
Maybe you want a table that contains a row for every minute in the day, and you want to use it to verify that a procedure has executed each minute, so you might cross three tables:
select
hour,
minute
from
hours CROSS JOIN minutes
Or you have a set of standard report specs that you want to apply to every month in the year:
select
specId,
month
from
reports CROSS JOIN months
The problem with maintaining these as views is that in most cases, you don't want a complete product, particularly with respect to clothes. You can add MINUS
logic to the query to remove certain combinations that you don't carry, but you might find it easier to populate a table some other way and not use a Cartesian product.
Also, you might end up trying the cross join on tables that have perhaps a few more rows than you thought, or perhaps your WHERE
clause was partially or completely missing. In that case, your DBA will notify you promptly of the omission. Usually he or she will not be happy.
Generate data for testing.