tag:blogger.com,1999:blog-7302956329008495023.post2252602221435161191..comments2022-01-04T06:37:33.013+00:00Comments on Databases and Performance: Optimizer Costing of JoinsJohn Bradyhttp://www.blogger.com/profile/08719865814813032071noreply@blogger.comBlogger1125tag:blogger.com,1999:blog-7302956329008495023.post-65506597484908084122012-07-09T04:40:30.736+01:002012-07-09T04:40:30.736+01:00Thus for 2 tables and 3 join methods the Optimizer...Thus for 2 tables and 3 join methods the Optimizer must cost 6 separate possible join combinations. For 3 tables this produces 6 different join combinations between them, each costed for the 3 join methods, for a total of 18 different possible join costs. For 4 tables it becomes 72 different joins to cost, and so on.<br /><br />when you calculate 3 tables join, the count may be not right, it seems 3*2*1*3*3=54, so 4 tables<br />4*3*2*1*3*3*3=24*27=648.Anonymousnoreply@blogger.com