Re: Looking for information on PostgreSQL Stored Procedures

On Sat, Dec 10, 2005 at 09:02:39PM -0600, Foster, Stephen wrote:
> I did see last week something on PLPGSQL and read through that. But
> there has to be something out there that goes in depth on the
> SQL/Function command set(Speaking of functions/procedures).

The standard functions are described in the "Functions and Operators"
chapter of the documentation. Here's a link to the latest version,
but use the documentation for the version you're running:

http://www.postgresql.org/docs/8.1/interactive/functions.html

SQL functions are documented in "Query Language (SQL) Functions":

http://www.postgresql.org/docs/8.1/interactive/xfunc-sql.html

> The biggest hole that I have; seems to be on Cursors; define and
> opening. I think the fetching and closing is pretty straight forward.
> But the Define and opening is causing some grief. Either I'm making to
> far too hard or I'm really have missing something silly.

What problems are you having? Without seeing what you're doing in
PostgreSQL it's difficult to say what's wrong.

In PL/pgSQL you can loop through query results without explicitly
using a cursor; see "Looping Through Query Results":

http://www.postgresql.org/docs/8.1/interactive/plpgsql-control-structures.html#PLPGSQL-RECORDS-ITERATING

[snip example]

> This is an example of the simple stored procedures like the ones I'm
> trying to migrate. PLPGSQL is ok but I thought it would run better in
> SQL.

SQL doesn't have control structures, so if you need conditionals
or loops then use a procedural language like PL/pgSQL or implement
the logic on the client side.

For the example you posted, the following query should have the same
effect (remove records with duplicate names, if I'm reading it right):

DELETE FROM mailinglist
WHERE id NOT IN (
SELECT DISTINCT ON (name) id
FROM mailinglist
ORDER BY name, id
);

I don't know how well this would perform on large data sets,
especially in older versions of PostgreSQL, but you could try it.
I'd recommend trying it first on a test table or in a transaction
that you can roll back in case it doesn't do what you want.

See the SELECT documentation for a description of the non-standard
DISTINCT ON clause that the above query uses:

http://www.postgresql.org/docs/8.1/interactive/sql-select.html

--
Michael Fuhr