Thread: ORDER BY case insensitive?
How do I get the rows sorted in a case insensitive way? I have some queries that basically fit the form: SELECT * FROM MyTable ORDER BY Name; When I view the results, all of the Name's that start with an upper case letter precede all of the Name's that start with a lower case letter. I want them all in alphabetic order, regardless of case. I've looked in PostgreSQL Introduction and Concepts by Bruce Momjian and in the FAQ at http://postgresql.overtone.org/docs/faq-english.html Thanks for your help. -- Bob Swerdlow Chief Operating Officer Transpose, LLC rswerdlow@transpose.com
SELECT * FROM MyTable ORDER BY lower(Name); Should do the trick. Jason Earl --- Bob Swerdlow <swerdlow@maine.rr.com> wrote: > How do I get the rows sorted in a case insensitive > way? > > I have some queries that basically fit the form: > SELECT * FROM MyTable ORDER BY Name; > When I view the results, all of the Name's that > start with an upper case > letter precede all of the Name's that start with a > lower case letter. I > want them all in alphabetic order, regardless of > case. > > I've looked in PostgreSQL Introduction and Concepts > by Bruce Momjian and in > the FAQ at > http://postgresql.overtone.org/docs/faq-english.html > > Thanks for your help. > > -- > Bob Swerdlow > Chief Operating Officer > Transpose, LLC > rswerdlow@transpose.com > > > > ---------------------------(end of > broadcast)--------------------------- > TIP 6: Have you searched our list archives? > > http://archives.postgresql.org __________________________________________________ Do You Yahoo!? NEW from Yahoo! GeoCities - quick and easy web site hosting, just $8.95/month. http://geocities.yahoo.com/ps/info1
My guess is that compared to the task of sorting
millions of names the fact that you have to lowercase
them first is not going to be a particular burden. No
matter what you do you are going to get a table scan
(unless you qualify your select with a where clause).
You can, however, create an index like:
create index MyTable_lower_idx on MyTable
(lower(name));
It won't help with your particular query, but it
certainly would help for queries like:
SELECT * FROM MyTable WHERE lower(name) = 'jason';
It is also possible to create a trigger that would
automatically lowercase information when it is
inserted or updated. Or even less high tech you can
make sure that all of your INSERTS and UPDATES use the
lower command like this:
INSERT into MyTable (name) VALUES (lower('VALUE'));
Jason
--- Bob Swerdlow <swerdlow@maine.rr.com> wrote:
> Thanks for the suggestion, Jason.
>
> A co-worker of mine, however, had this response:
> Yes, but my guess is that that will first
> convert all million (or
> whatever) records to upper case, and then physically
> sort them. It won't be
> able to make use of the index.
>
> To make this efficient, do we need to uppercase all
> of the data before
> adding to the table? (yuk)
>
> - Bob
>
>
> ----- Original Message -----
> From: "Jason Earl" <jdearl@yahoo.com>
> To: "Bob Swerdlow" <swerdlow@maine.rr.com>;
> <pgsql-sql@postgresql.org>
> Sent: Thursday, October 04, 2001 3:47 PM
> Subject: Re: [SQL] ORDER BY case insensitive?
>
>
> > SELECT * FROM MyTable ORDER BY lower(Name);
> >
> > Should do the trick.
> >
> > Jason Earl
> >
> > --- Bob Swerdlow <swerdlow@maine.rr.com> wrote:
> > > How do I get the rows sorted in a case
> insensitive
> > > way?
> > >
> > > I have some queries that basically fit the form:
> > > SELECT * FROM MyTable ORDER BY Name;
> > > When I view the results, all of the Name's that
> > > start with an upper case
> > > letter precede all of the Name's that start with
> a
> > > lower case letter. I
> > > want them all in alphabetic order, regardless of
> > > case.
> > >
> > > I've looked in PostgreSQL Introduction and
> Concepts
> > > by Bruce Momjian and in
> > > the FAQ at
> > >
> http://postgresql.overtone.org/docs/faq-english.html
> > >
> > > Thanks for your help.
> > >
> > > --
> > > Bob Swerdlow
> > > Chief Operating Officer
> > > Transpose, LLC
> > > rswerdlow@transpose.com
> > >
> > >
> > >
> > > ---------------------------(end of
> > > broadcast)---------------------------
> > > TIP 6: Have you searched our list archives?
> > >
> > > http://archives.postgresql.org
> >
> >
> > __________________________________________________
> > Do You Yahoo!?
> > NEW from Yahoo! GeoCities - quick and easy web
> site hosting, just
> $8.95/month.
> > http://geocities.yahoo.com/ps/info1
> >
>
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On Thu, 4 Oct 2001, Jason Earl wrote: > My guess is that compared to the task of sorting > millions of names the fact that you have to lowercase > them first is not going to be a particular burden. No > matter what you do you are going to get a table scan > (unless you qualify your select with a where clause). > > You can, however, create an index like: > > create index MyTable_lower_idx on MyTable > (lower(name)); > > It won't help with your particular query, but it > certainly would help for queries like: Current sources do (and I think older sources may) consider such an index to replace the sort step. On a test table with 100000 strings, explain shows an index scan for the lower(<col>) ordering and a seq scan/sort for <col> ordering. At this point there's actually a performance gain for the lower() index scan.
Jason Earl wrote: > > You can, however, create an index like: > > create index MyTable_lower_idx on MyTable > (lower(name)); > > It won't help with your particular query, but it > certainly would help for queries like: > > SELECT * FROM MyTable WHERE lower(name) = 'jason'; > How would PostgreSQL know to use the index MyTable_lower_idx when I do a ... SELECT * FROM MyTable WHERE lower(name) LIKE 'jas%'; -- Keith Gray Technical Development Manager Heart Consulting Services P/L mailto:keith@heart.com.au
Keith Gray <keith@heart.com.au> writes:
> How would PostgreSQL know to use the index
> MyTable_lower_idx when I do a ...
> SELECT * FROM MyTable WHERE lower(name) LIKE 'jas%';
The same way it knows to use any other index: it matches up the things
mentioned in the WHERE clause with the available indexes, and then sees
whether the clauses they are mentioned in are comparisons that the index
can help with. In this case the "thing" mentioned is "function(column)"
rather than just "column", but otherwise it's just like a simple index.
regards, tom lane
Thanks for the suggestion, Jason. A co-worker of mine, however, had this response: Yes, but my guess is that that will first convert all million (or whatever) records to upper case, and then physically sort them. It won't be able to make use of the index. To make this efficient, do we need to uppercase all of the data before adding to the table? (yuk) - Bob ----- Original Message ----- From: "Jason Earl" <jdearl@yahoo.com> To: "Bob Swerdlow" <swerdlow@maine.rr.com>; <pgsql-sql@postgresql.org> Sent: Thursday, October 04, 2001 3:47 PM Subject: Re: [SQL] ORDER BY case insensitive? > SELECT * FROM MyTable ORDER BY lower(Name); > > Should do the trick. > > Jason Earl > > --- Bob Swerdlow <swerdlow@maine.rr.com> wrote: > > How do I get the rows sorted in a case insensitive > > way? > > > > I have some queries that basically fit the form: > > SELECT * FROM MyTable ORDER BY Name; > > When I view the results, all of the Name's that > > start with an upper case > > letter precede all of the Name's that start with a > > lower case letter. I > > want them all in alphabetic order, regardless of > > case. > > > > I've looked in PostgreSQL Introduction and Concepts > > by Bruce Momjian and in > > the FAQ at > > http://postgresql.overtone.org/docs/faq-english.html > > > > Thanks for your help. > > > > -- > > Bob Swerdlow > > Chief Operating Officer > > Transpose, LLC > > rswerdlow@transpose.com > > > > > > > > ---------------------------(end of > > broadcast)--------------------------- > > TIP 6: Have you searched our list archives? > > > > http://archives.postgresql.org > > > __________________________________________________ > Do You Yahoo!? > NEW from Yahoo! GeoCities - quick and easy web site hosting, just $8.95/month. > http://geocities.yahoo.com/ps/info1 >