On 10 Mar 2003, at 16:31, Tab Alleman wrote: > I was thinking if you do a select on a char[50] and the whole field > is indexed, wouldn't the search algorithm know exactly where to go > to look for a match, as opposed to - if only the first 20 characters > are indexed - finding all of the possible values that match the > first 20 and then having to go through all of them looking for a > match?
Certainly the distribution of data values would make a difference, but it would seem to be an unusual set of data that would have a huge number of names that matched in the first 20 characters but differed after that point. > It would seem like, from what I know of indexes, if the whole > field is indexed, only one disk read should be necessary since > it would go right to that row the first time. I believe Benjamin was talking about the disk reads necessary to get the index, not to get the record itself. [Filter fodder: SQL] -- Keith C. Ivey <[EMAIL PROTECTED]> Tobacco Documents Online http://tobaccodocuments.org Phone 202-667-6653 --------------------------------------------------------------------- Before posting, please check: http://www.mysql.com/manual.php (the manual) http://lists.mysql.com/ (the list archive) To request this thread, e-mail <[EMAIL PROTECTED]> To unsubscribe, e-mail <[EMAIL PROTECTED]> Trouble unsubscribing? Try: http://lists.mysql.com/php/unsubscribe.php
