On Sun, Apr 6, 2008 at 9:57 PM, Eric Bergen <[EMAIL PROTECTED]> wrote: > I don't see what the issue is. As Jay said the row counts in explain > outputs are estimates. When running an explain query MySQL asks the > storage engine how many rows it thinks are between a set of values for > an index. Different storage engines use different methods to calculate > row count. Both innodb and myisam estimate the row count based on > statistics they keep on the distribution of keys in an index. MyISAM > is more accurate than innodb with it's row count because of how it > keeps statistics. Analyze table on a myisam table will count the > number of unique values in an index > (myisam/mi_check:update_key_parts). Innodb samples the key > distribution in 8 different pages per index and does some calculations > based on the tree structure of those pages (details > innobase/btr/btr0cur.c:btr_estimate_number_of_different_key_vals).
Thank you! I spent a bit trying to find details about how row counts were computed, but with no luck (I probably did not know how to know how to look...). Could the alternative I had proposed be accurate at all? -- Rob Wultsch [EMAIL PROTECTED] wultsch (aim) -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
