Difference between function and procedure?

On 7/19/06, Anastasios Hatzis <ahatzis@gmx.net> wrote:

Hi,

I'm diving more into depth of the features outside the typical table
stuff, which I usually need.

I wrote a trigger that fires a function written in PL/Python, both works
fine so far.

But as I browsed my database via pgAdmin3 I recognized that there is
also 'Procedures' under 'public' available, but empty yet. Trying to
create a procedure resulted in the same SQL statement like creating a
function (CREATE FUNCTION ...). I couldn't see any difference. Also
didn't find in the PostgreSQL manual if there is a difference between
functions and procedures. Are there any at all?

there are differences. PostgreSQL only really supports functions and
on the lists they are used interchangably. on the -hacker list about
a year back there was a good discussion about implementing true SP and
why they would be needed.

mainly, SP are not externally transactional, making them useful for
maintenance type work, such as vacuum (cant be run from inside a
transaction) or multiple statement data load via 'copy' commands.

i thnk (not sure) that SP can not be inlined into queries like
functions. this would be an important distinction.

merlin

Merlin Moncure wrote:

there are differences. PostgreSQL only really supports functions and
on the lists they are used interchangably. on the -hacker list about
a year back there was a good discussion about implementing true SP and
why they would be needed.

mainly, SP are not externally transactional, making them useful for
maintenance type work, such as vacuum (cant be run from inside a
transaction) or multiple statement data load via 'copy' commands.

i thnk (not sure) that SP can not be inlined into queries like
functions. this would be an important distinction.

Merlin,

thank you for clarifying this. So, given your hint, I didn't miss SP
until now, but this will probably change in future. ;-)

Anastasios

I saw the same behavior with Functions and Procedures. At first, I could
not tell what made one go into the Function folder and one go into the
Procedure one. The one thing that clearly distinguishes a Procedure (to be
placed into the Procedures folder in PgAdminIII) is if you include an OUT
parameter. The first time I wrote a Function with an OUT parameter, I could
not find it in the functions folder. I thought at first that it didn't
compile. Then I noticed it in the Procedures folder. Probably a lot of
other characteristics that make it different, but that is at least one. :)

-Paul