Re: [SQL] User-defined error messages/codes

[Yes, I know it's bad style to reply to one's own posts.  Oh well.]

On Thu, Jan 27, 2000 at 06:13:28PM -0500, Vince Gonzalez wrote:
> Is it possible to create user-defined error messages in functions?
> For example, I'd like for an update to a table to fail with a message like
> 'You need to check your privileges' as opposed to 'Permission Denied'.    
> I'd like to avoid parsing the messages actually returned by the server,   
> as these could change from revision to revision.  Should I do this by     
> crafting each function to return an error code that I define, and then    
> use that code to index a table?  I'm interested to hear any solutions     
> people may have come up with.                                             
> 
> I seem to remember there being some sort of exception facility, but I
> can't remember where I may have seen it (or I could be crazy).       

Man, its funny how posting a question to a mailing list makes it easier
to find the answer on your own. :)  After re-scanning the programmer's
manual, I found info on using RAISE to throw messages:

test=> CREATE TABLE "test" ("a" int4);
CREATE
test=> 
test=> CREATE FUNCTION "throwit" ( ) RETURNS int4 AS '
test'> DECLARE
test'>         arecord RECORD;
test'> BEGIN
test'>         select a into arecord from test where a = 5;
test'>         if not found then
test'>         raise exception ''five not found'';
test'>         end if;
test'>         return 5;
test'> END;
test'> ' LANGUAGE 'plpgsql';
CREATE
test=> 
test=> INSERT INTO test (a) values (1);
INSERT 2168921 1
test=> INSERT INTO test (a) values (2);
INSERT 2168922 1
test=> INSERT INTO test (a) values (3);
INSERT 2168923 1
test=> INSERT INTO test (a) values (4);
INSERT 2168924 1
test=> select throwit();
ERROR:  five not found
test=>

Lovely.  Now, I still am not sure how to proceed with my first question,
of how to handle user privileges in a way that does not require me to actually
attempt an operation to find out if it will succeed.

--vince