Обсуждение: Natural sort order
Morning... What is the fastest way to achieve natural ordering from queries? I found a function at: http://2kan.tumblr.com/post/361326656/postgres-natural-ordering But it increases the query time from around 0.4msecs to 74msecs... Might be not much if occasional queries are made..but I use it for building up a hierarchical tree menu in a web application where every msecs counts (o; cheers richard
If you use btrsort(column) from the example, you can just create a functional index on this expression. CREATE INDEX mytable_column_btrsort_idx ON mytable( btrsort(column) ); this can help. 2011/12/17 Richard Klingler <richard@klingler.net>: > Morning... > > What is the fastest way to achieve natural ordering from queries? > > I found a function at: > http://2kan.tumblr.com/post/361326656/postgres-natural-ordering > > But it increases the query time from around 0.4msecs to 74msecs... > Might be not much if occasional queries are made..but I use it for > building > up a hierarchical tree menu in a web application where every msecs > counts (o; > > > cheers > richard > > > -- > Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-sql
Took some time until I could try out this... But as soon I want to create the fcuntion based index it tells me: Error : ERROR: functions in index expression must be marked IMMUTABLE Deleteing the sort function and recreating with the IMMUTABLE attribute gives the same error.. Here the functions: CREATE FUNCTION btrsort_nextunit(text) RETURNS text AS $$SELECT CASE WHEN $1 ~ '^[^0-9]+' THEN COALESCE( SUBSTR($1, LENGTH(SUBSTRING($1 FROM '[^0-9]+'))+1 ), '' ) ELSE COALESCE( SUBSTR( $1, LENGTH(SUBSTRING($1 FROM '[0-9]+'))+1), '' ) END $$ LANGUAGE SQL IMMUTABLE; CREATE FUNCTION btrsort(text) RETURNS text AS $$SELECT CASE WHEN char_length($1)>0 THEN CASE WHEN $1 ~ '^[^0-9]+'THEN RPAD(SUBSTR(COALESCE(SUBSTRING($1 FROM '^[^0-9]+'), ''), 1, 12), 12, ' ') || btrsort(btrsort_nextunit($1)) ELSE LPAD(SUBSTR(COALESCE(SUBSTRING($1 FROM '^[0-9]+'), ''), 1, 12), 12, '') || btrsort(btrsort_nextunit($1)) END ELSE $1 END ; $$ LANGUAGE SQL IMMUTABLE; And the index creation: create index port_name_btrsort_index on port(btrsort(name)); Which should speed up my query: select * from port where name not like '%Z' order by btrsort(name) asc cheers richard On Sat, 17 Dec 2011 16:16:07 +0100, Filip Rembiałkowski wrote: > If you use btrsort(column) from the example, you can just create a > functional index on this expression. > > CREATE INDEX mytable_column_btrsort_idx ON mytable( btrsort(column) ); > > this can help. > > > > > > 2011/12/17 Richard Klingler <richard@klingler.net>: >> Morning... >> >> What is the fastest way to achieve natural ordering from queries? >> >> I found a function at: >> http://2kan.tumblr.com/post/361326656/postgres-natural-ordering >> >> But it increases the query time from around 0.4msecs to 74msecs... >> Might be not much if occasional queries are made..but I use it for >> building >> up a hierarchical tree menu in a web application where every msecs >> counts (o; >> >> >> cheers >> richard >> >> >> -- >> Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org) >> To make changes to your subscription: >> http://www.postgresql.org/mailpref/pgsql-sql > > -- > Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-sql
Richard Klingler <richard@klingler.net> writes:
> Took some time until I could try out this...
> But as soon I want to create the fcuntion based index it tells me:
> Error : ERROR: functions in index expression must be marked IMMUTABLE
FWIW, this example works fine for me. Maybe you have some weird
user-defined version of substr() or ~ that isn't immutable?
regards, tom lane
Actually got it figured...for some reason it had the function twice (o; But with or without function index the time to query stays the same...around 110msec for 24 results... cheers richard On Wed, 29 Feb 2012 11:08:46 -0500, Tom Lane wrote: > Richard Klingler <richard@klingler.net> writes: >> Took some time until I could try out this... >> But as soon I want to create the fcuntion based index it tells me: >> Error : ERROR: functions in index expression must be marked IMMUTABLE > > FWIW, this example works fine for me. Maybe you have some weird > user-defined version of substr() or ~ that isn't immutable? > > regards, tom lane > > -- > Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-sql
The fastest way is to create a ref table with all possible entries, ordered with an additionnal numerical column, indexing it and make a join from your table to this ref table. A + Le 17/12/2011 11:33, Richard Klingler a écrit : > Morning... > > What is the fastest way to achieve natural ordering from queries? > > I found a function at: > http://2kan.tumblr.com/post/361326656/postgres-natural-ordering > > But it increases the query time from around 0.4msecs to 74msecs... > Might be not much if occasional queries are made..but I use it for > building > up a hierarchical tree menu in a web application where every msecs > counts (o; > > > cheers > richard > > -- Frédéric BROUARD - expert SGBDR et SQL - MVP SQL Server - 06 11 86 40 66 Le site sur le langage SQL et les SGBDR : http://sqlpro.developpez.com Enseignant Arts & Métiers PACA, ISEN Toulon et CESI/EXIA Aix en Provence Audit, conseil, expertise, formation, modélisation, tuning, optimisation *********************** http://www.sqlspot.com *************************