Thanks a lot Tom, don't know why this email was delivered even today, it was sent yesterday and Dr. Hipp already replied me. Anyway… thanks a lot for your detailed explanation, I really appreciate.
-- Marco Bambini http://www.sqlabs.com On Jan 11, 2012, at 4:06 PM, BareFeetWare wrote: > Hi Marco, > > In reply to: > >> From the PRAGMA index_info documentation: >> This pragma returns one row each column in the named index. The first column >> of the result is the rank of the column within the index. The second column >> of the result is the rank of the column within the table. The third column >> of output is the name of the column being indexed. >> >> I am particularly interested in the rank fields … what does rank really >> means here? >> Is there a lower/upper bound to this rank value? > > If you have an index that is for multiple columns, the "rank of the column > within the index" (which is labeled in the output as "seqno") tells you the > order of those columns in the index. For example: > > create table Person > ( ID integer primary key not null > , "First Name" text collate nocase > , "Last Name" text collate nocase > , "Email" text collate nocase > ) > ; > create index "Person index by First, Last" > on "Person" ("First Name", "Last Name") > ; > create index "Person index by Email, First" > on "Person" ("Email", "First Name") > ; > > Then: > > pragma index_info ('Person index by First, Last') > > gives: > > seqno cid name > 0 1 First Name > 1 2 Last Name > > which means that this indexes columns "First Name" and "Last Name" in that > order (ie 0, 1). > > And > > pragma index_info ('Person index by Email, First') > > gives: > > seqno cid name > 0 3 Email > 1 1 First Name > > which means that this indexes columns "Email" and "First Name" in that order > (ie 0, 1). > > Tom > > Tom Brodhurst-Hill > BareFeetWare > > -- > iPhone/iPad/iPod and Mac software development, specialising in databases > develo...@barefeetware.com > -- > Twitter: http://twitter.com/barefeetware/ > Facebook: http://www.facebook.com/BareFeetWare > > _______________________________________________ > sqlite-users mailing list > sqlite-users@sqlite.org > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
