On Thu, Apr 2, 2009 at 12:01 PM, Igor Tandetnik <[email protected]> wrote: > baxy77bax <[email protected]> wrote: >> i need some help to see if i understood the point about indexing. >> >> if i have 2 tables. each table has 2 columns. and now i want to join >> those tables through one column in each table: >> >> example >> T1 >> C1 C2 >>> >> +--+ >> | >> T2 | >> C1 C2 >> >> let say the columns in question are C1(t1) and C2(t2) >> first question: >> can i create index X1 in both columns C1(t1) and C2(t2) ? > > No. But you can of course create two indexes, one on T1(C1) and another > on T2(C2). Though you would only need one of them to speed up the join. > >> and what is the >> actual gain when i create indexes. > > The same you get from an index printed at the end of a textbook: it > allows you to quickly look up a term and jump to the right page.
See http://www.mail-archive.com/[email protected]/msg37474.html for a very, very nice explanation from Igor of how indexes work. The explanation uses the same metaphor of an index in a text book as described above by Igor. > > Igor Tandetnik > > > -- Puneet Kishor http://www.punkish.org/ Nelson Institute for Environmental Studies http://www.nelson.wisc.edu/ Carbon Model http://carbonmodel.org/ Open Source Geospatial Foundation http://www.osgeo.org/ Sent from Madison, WI, United States _______________________________________________ sqlite-users mailing list [email protected] http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
