Re: Way to use count() and LIMIT?

I see two options but they may not be the correct ones but here goes.

1) Either put a subselect in your select clause that gets the number of
rows

2) Create a plpgsql function that returns the number of rows and put it in
your  select clause.

Both add a little more load to your query but they will give you the
answers. Use explain to figure out which one is less intensive

My 2 cents

Darren

Darren Ferguson
Software Engineer
Openband

On Tue, 18 Dec 2001, Joe Koenig wrote:

> I was currently using a LIMIT and OFFSET to move through 20 at a time. I
> need to know the total for 2 reasons:
>
> 1) To display it to the user
> 2) So my script knows whether or not to put a next button.
>
> I was hoping I could avoid 2 queries. Is the best way to do this to just
> use LIMIT and OFFSET in one query and just do a count() in the first?
> Does using a cursor offer any benefit over the LIMIT and OFFSET method? Thanks,
>
> Joe
>
> "SHELTON,MICHAEL (Non-HP-Boise,ex1)" wrote:
> >
> > You will also need to do a select first to get the total count.  You can
> > store it in a var then pass it back to the user for each 20 or whatever
> > amount (so each time they know total) or pass it once, then create cursor.
> >
> > You can also use LIMIT with OFFSET to do a simple select each time for 20 at
> > a time.
> >
> > -----Original Message-----
> > From: Jason Earl [mailto:jason.earl@simplot.com]
> > Sent: Tuesday, December 18, 2001 12:27 PM
> > To: joe@jwebmedia.com
> > Cc: pgsql-general@postgresql.org
> > Subject: Re: [GENERAL] Way to use count() and LIMIT?
> >
> > Sure, just declare a cursor.  Here's a simple one that I use:
> >
> >     DECLARE raw_data CURSOR FOR
> >     SELECT
> >         (SELECT pc FROM curpack1 WHERE curpack1.dt <= caseweights1.dt
> >          ORDER BY curpack1.dt DESC LIMIT 1) AS "pc",
> >         dt::date AS "date",
> >         dt::time AS "time",
> >         weight AS "weight"
> >         FROM caseweights1
> >         WHERE dt >= '%s' AND
> >         dt < '%s'
> >         ORDER BY dt;
> >
> > Then you simply fetch from this cursor (like so):
> >
> >     FETCH FORWARD 20 IN raw_data;
> >
> > And you close it with a simple:
> >
> >     CLOSE raw_data;
> >
> > Jason
> >
> > Joe Koenig <joe@jwebmedia.com> writes:
> >
> > > Is there a way to structure a query so you can only run 1 query, get the
> > > full number of rows that would be returned, but then use LIMIT to step
> > > through in groups of 20? For example, a search in my CD's/Rock section
> > > will return 53,000 results. I want to give the user the number of total
> > > results, but also use LIMIT to go through 20 at a time? Does this
> > > require 2 queries? Thanks,
> > >
> > > Joe
> > >
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