What happens , when cross join is created between query subjects

[inu]

Hi
Please tell me , cross join is good for performance, or not.
When we need to take help of cross joins.
What it actually does, if created.


Thanks
Inam

[MFGF]

Hi
Please tell me , cross join is good for performance, or not.
When we need to take help of cross joins.
What it actually does, if created.


Thanks
Inam

No - cross joins are generally not at all good for performance. Consider a scenario:

You have two tables, each containing only 1000 rows of data. Not big, by any means. If you enable a cross-join between them, you effectively join every row of the first table to every row of the second table. That will return a result set of 1,000,000 rows - which is rather larger than you might expect. There are certain occasions when cross-joins might be useful, but they are less common than you might imagine.

MF.

[linbai]

No - cross joins are generally not at all good for performance. Consider a scenario:

You have two tables, each containing only 1000 rows of data. Not big, by any means. If you enable a cross-join between them, you effectively join every row of the first table to every row of the second table. That will return a result set of 1,000,000 rows - which is rather larger than you might expect. There are certain occasions when cross-joins might be useful, but they are less common than you might imagine.

MF.

+1 good
may be ETL is a good way to cross-join tables.