Edson Carlos Ericksson Richter wrote: > If query is covered by index, is not more fast to do a "index scan"?
Not at all. If the amount of pages to read on both, the index and the table, is the same it make no differences. > I know that MS SQL Server does some nice optimizations using > "indexes that > cover queries" (all fields that make part of the query exists > on the index). > This is a true (in MS SQL case) because indexes pages, that > will have less > fields that table (not case in example from Jason) will have > less pages to > read from disks, improving IO performance. And so did SAP DB. We call it "index only strategies". The explain indicates such a strategy with the '*' in the 'O' column. > Exists any PDFs that explains, in details, strategies for performance > optimizations and how SapDB does his choices? Have a look at "Optimizer: SAP DB 7.4" http://www.sapdb.org/7.4/htmhelp/fb/36fe3b34334a7be10000000a114084/frameset.htm Kind regards, Holger SAP Labs Berlin _______________________________________________ sapdb.general mailing list [EMAIL PROTECTED] http://listserv.sap.com/mailman/listinfo/sapdb.general
