HI,
I have a general question on the book from Dan Tow on "SQL Tuning".
He recommends in chapter 6 "Deducing the best execution plan" a Standard heuristic join order:
1.) Drive first to the table with the best (nearest to Zero) filter ratio
Why does the filter Ratio determine the first table?
Why does not the table with the lowest number of rows (including application of a filter) determine the first table?
Example:
Table A has 100Mio rows and a filter might result in 10Mio rows (filters down to 10%)
Table B has 20Mio rows and a filter might result in 5Mio rows (filters down to 25%)
According to the book, table A has the best filter and therefore determines the start. But table B would have less rows after applying the filter.