Stored procedures and "pseudo" fields..

I also posted this to the general list, which might not have been a
suitable forum.

--
I have recently ventured into the exciting world of stored procedures,
but I have now become lost.

Background:

Am currently working on access control in a web application. My goal
is to process access control on the SQL level. This way if a row is in
the result set, you have access to it, if not, you don't.

Problem:

My stored procedure "acl_check()" takes two integers as parameters.
Param1 is the object id to check acl on, Param 2 is the object id of
the user currently using the system. The procedure returns a positive
number (1 or 3 ) if you have some kind of access to the object. As one
might understand I want the returned value from the acl_check()
procedure to be a part of the result set.

Kinda like this:

SELECT *, acl_check( objects.obid, <user_id> ) AS mode FROM objects
WHERE mode > 0;

This gives me a: ERROR: column "mode" does not exist

If I remove the "mode > 0" logic, I get a result set with mode in it as
expected. Why cant I do logic tests with the mode "field" ?

I tried a different approach with a different error:

SELECT * FROM objects, acl_check( objects.obid, 32 ) as mode WHERE mode > 0;

This gives me a: ERROR: function expression in FROM may not refer to
other relations of same query level.

Here objecs.obid is unknown i suppose, but if I enter "10" as the
first param using the mode "field" in a logic statement works.

I would appreciate any hints to a workaround which would enable me to
accomplish my scenario.

Best regards,

L.E.Thorsplass

On 2004-07-20 15:34, Użytkownik Lars Erik Thorsplass napisał:

My stored procedure "acl_check()" takes two integers as parameters.
Param1 is the object id to check acl on, Param 2 is the object id of
the user currently using the system. The procedure returns a positive
number (1 or 3 ) if you have some kind of access to the object. As one
might understand I want the returned value from the acl_check()
procedure to be a part of the result set.

Kinda like this:

SELECT *, acl_check( objects.obid, <user_id> ) AS mode FROM objects
WHERE mode > 0;

This gives me a: ERROR: column "mode" does not exist

You can't access column output alias in where clause. Instead you have
to use your function twice:

SELECT *, acl_check( objects.obid, <user_id> ) AS mode FROM objects
WHERE acl_check( objects.obid, <user_id> ) > 0;

Regards,
Tomasz Myrta

В Втр, 20.07.2004, в 15:57, Tomasz Myrta пишет:

On 2004-07-20 15:34, Użytkownik Lars Erik Thorsplass napisał:

My stored procedure "acl_check()" takes two integers as parameters.
Param1 is the object id to check acl on, Param 2 is the object id of
the user currently using the system. The procedure returns a positive
number (1 or 3 ) if you have some kind of access to the object. As one
might understand I want the returned value from the acl_check()
procedure to be a part of the result set.

Kinda like this:

SELECT *, acl_check( objects.obid, <user_id> ) AS mode FROM objects
WHERE mode > 0;

This gives me a: ERROR: column "mode" does not exist

You can't access column output alias in where clause. Instead you have
to use your function twice:

SELECT *, acl_check( objects.obid, <user_id> ) AS mode FROM objects
WHERE acl_check( objects.obid, <user_id> ) > 0;

and if you properly marked the function STABLE and I am not mistaken,
then PostgreSQL is smart enough to execute the function only once per
row.

--
Markus Bertheau <twanger@bluetwanger.de>

On Tue, 2004-07-20 at 04:43, Lars Erik Thorsplass wrote:

I have recently ventured into the exciting world of stored procedures,
but I have now become lost.

Background:

Am currently working on access control in a web application. My goal
is to process access control on the SQL level. This way if a row is in
the result set, you have access to it, if not, you dont.

Problem:

My stored procedure "acl_check()" takes two integers as parameters.
Param1 is the object id to check acl on, Param 2 is the object id of
the user currently using the system. The procedure returns a positive
numer (1 or 3 ) if you have some kind of access to the object. As one
might understand I want the returned value from the acl_check()
procedure to be a part of the result set.

Kinda like this:

SELECT *, acl_check( objects.obid, <user_id> ) AS mode FROM objects
WHERE mode > 0;

Here's the problem. In order to do the select, the query first needs to
run the where clause. I.e.:

select a as test from table where a > 50;

works, but

select a as test from table where test > 50;

fails. The reason is that when the where clause fires first, there IS
no test yet, as it hasn't been materialized. what you need to do is:

select custom_function(a,b) from table where custom_function(a,b) > 0;

On Tue, 20 Jul 2004 09:45:06 -0600, Scott Marlowe <smarlowe@qwest.net> wrote:

Kinda like this:

SELECT *, acl_check( objects.obid, <user_id> ) AS mode FROM objects
WHERE mode > 0;

Here's the problem. In order to do the select, the query first needs to
run the where clause. I.e.:

select a as test from table where a > 50;

works, but

select a as test from table where test > 50;

fails. The reason is that when the where clause fires first, there IS
no test yet, as it hasn't been materialized. what you need to do is:

select custom_function(a,b) from table where custom_function(a,b) > 0;

Thanks for clearing that up. I just hoped there was some magic I could
sprinkle on my query to get away from the extra overhead of running
the procedure twice :)

Best regards..

L.E.Thorsplass

Lars Erik Thorsplass wrote:

On Tue, 20 Jul 2004 09:45:06 -0600, Scott Marlowe <smarlowe@qwest.net> wrote:

Kinda like this:

SELECT *, acl_check( objects.obid, <user_id> ) AS mode FROM objects
WHERE mode > 0;

Here's the problem. In order to do the select, the query first needs to
run the where clause. I.e.:

select a as test from table where a > 50;

works, but

select a as test from table where test > 50;

fails. The reason is that when the where clause fires first, there IS
no test yet, as it hasn't been materialized. what you need to do is:

select custom_function(a,b) from table where custom_function(a,b) > 0;

Thanks for clearing that up. I just hoped there was some magic I could
sprinkle on my query to get away from the extra overhead of running
the procedure twice :)

Best regards..

L.E.Thorsplass

Pretty late, I know, but just for the record, AFAICS there is this magic as
SELECT * FROM (
SELECT *, acl_check( objects.obid, <user_id> ) AS mode FROM objects
) AS foo WHERE mode > 0;

Regards, Christoph