On 29/11/2011 05:49, Alex Peshkoff wrote: > On 11/29/11 04:42, Claudio Valderrama C. wrote: >>> -----Original Message----- >>> From: Adriano dos Santos Fernandes [mailto:adrian...@gmail.com] >>> Sent: Lunes, 28 de Noviembre de 2011 16:08 >>> No. It happens with large varchar column. So it turns back to my >>> question: can we describe a column with a length we know will fit and >>> will have no side effects other than just being described different? >> I tried to do that in my first implementation, but then we have a problem: >> substring with parameters. Should >> substring(s from :n for :m) >> use the max length from "s" and >> substring(s from 5 for 10) >> use 10 if length(s)> 10 ??? >> >> >>> Sure, a different descriptor would have no side effect in the >>> index, but >>> a change would be valid for any usage of substring. >> Yes and the problem is that for an expression index to be used, AFAIK the >> search expression should be identical, hence if somebody wants to use an >> index created as >> CREATE INDEX IDX1 ON tbl_test COMPUTED BY (CAST(SUBSTRING(col1 from 1 for >> 20) as varchar(20))) >> the user should write >> where CAST(SUBSTRING(col1 from 1 for 20) as varchar(20)) = 'something' >> >> Not very elegant. > But taking into an account other considerations is the only correct. > > May be we can think about builting function like index_expr. That's just > raw idea, but may be something like > INDEX_EXPR(ALIAS.indexName) > is better than >
This is up to the user to create a function then. No need for this support in the engine. Adriano ------------------------------------------------------------------------------ All the data continuously generated in your IT infrastructure contains a definitive record of customers, application performance, security threats, fraudulent activity, and more. Splunk takes this data and makes sense of it. IT sense. And common sense. http://p.sf.net/sfu/splunk-novd2d Firebird-Devel mailing list, web interface at https://lists.sourceforge.net/lists/listinfo/firebird-devel
