The thing is, you would have sql that have LIMIT appended at the end like
select * from sometable limit 25
but what if you wanted to know how many rows would have been returned if it was not limited?
the trivial approach is
select count(*) from sometable
and then issuing query with limit on it.
This is slower solution.
here is the way to do it in a better way
select sql_calc_found_rows * from sometable limit 25; select found_rows();
Right after execution the select with sql_calc_found_rows, we would get the ‘would have been’ value on the second query.