Neulinger, Friday, November 15, 2002, 7:25:27 PM, you wrote: NN> Assume I have a mysql table (myisam most likely) with a few hundred NN> thousand rows in it. One of the columns indicates success or failure. NN> 99.9% of the rows will have "0" in that column. But a small number will NN> have 1. I need to be able to fetch those rows quickly, without slowing NN> everything else down, but ideally without doing a full table scan.
NN> I can create an index on that column, but I am under the impression that NN> this a really bad/slow type of index to create/maintain, since one of NN> the values will cover most of the table. NN> I'd like to be able to say something like: NN> create index failures on dumps(status) where status!=0; NN> If the sql query being run isn't compatible with the restriction on the NN> index, then it cannot be used. For example, if I query for status=2, it NN> would be ok, but status=0 would not be able to use the index. Simpler NN> may be to only allow the index to be used if the query contains exactly NN> the same restriction. i.e. the "where status !=0" index could only be NN> used if I had "status != 0" in my select query. NN> Or alternatively, if you can suggest some other means for accomplishing NN> this efficiently... NN> (Yes, I know I can make a temporary or results table updated NN> periodically, which I will likely do in the meantime, but would be nice NN> to have an efficient way of accomplishing this with live data.) If I've got you right status can have values 0 or 1. In this case you can just use " SELECT ... WHERE status=1 .." (index wil be used) or "SELECT .. WHERE status=0 .." (index will not be used, because scan the whole table will be faster to retrieve 99,9% of rows) depends on what you want to get. -- For technical support contracts, goto https://order.mysql.com/?ref=ensita This email is sponsored by Ensita.net http://www.ensita.net/ __ ___ ___ ____ __ / |/ /_ __/ __/ __ \/ / Egor Egorov / /|_/ / // /\ \/ /_/ / /__ [EMAIL PROTECTED] /_/ /_/\_, /___/\___\_\___/ MySQL AB / Ensita.net <___/ www.mysql.com --------------------------------------------------------------------- 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
