Why does paginate call the database twice?

[eluser]gh0st[/eluser]
I thought you had to do the query (regardless of complexity) twice to get the right number of rows back?

Let's say you had a complex query involving some INNER JOIN's... don't you have to do a num_rows on the INNER JOINed query so that you get the correct number of records?

Or.. perhaps you have a complex, filtered query (with no INNER JOINs, etc), don't you still need to do a num_rows on the complex query, so that you get the correct number of records?

Thanks