Обсуждение: plpgsql variable substitution problem ...

[Hopefully the correct list this time :)]

Howdy.  Creating a function to access different tables depending
on the arguments. However, am having excessive problems.

Current code is as follows:

CREATE FUNCTION access(varchar,varchar) RETURNS INT4 AS '
DECLARE       lcl_field ALIAS FOR $1;       lcl_table ALIAS FOR $2;       lcl_max INT;
BEGIN

SELECT max(lcl_field) INTO lcl_max FROM lcl_table;

RETURN lcl_max;

END;

' LANGUAGE 'plpgsql';

However, if I execute the following code

SELECT getsequence('f1','t1');

I get an error:
 psql:sequence.db:35: ERROR:  parser: parse error at or near "$2"

(What I really want is to execute a "SELECT max(f1) FROM f2")

The output from the postmaster is:

000528.19:45:45.682  [9553] CommitTransactionCommand
000528.19:45:45.713  [9553] StartTransactionCommand
000528.19:45:45.713  [9553] query: SELECT access('f1','t1'));
000528.19:45:45.717  [9553] ProcessQuery
000528.19:45:45.725  [9553] query: SELECT  max( $1 ) FROM  $2
000528.19:45:45.726  [9553] ERROR:  parser: parse error at or near "$2"
000528.19:45:45.726  [9553] DEBUG:  Last error occured while executing PL/pgSQL function getsequence
000528.19:45:45.726  [9553] DEBUG:  line 6 at select into variables
000528.19:45:45.726  [9553] AbortCurrentTransaction

Any ideas? I've fiddled with the variables and procedures a few
times but I can't quite get a breakthrough.

tia,
  -Greg

------------------------------------------------------------------
www.geelong.com                                       Greg Wickham  P.O. Box 1426
greg@geelong.com
Geelong VIC 3220                             Ph: (+61 407) 854 566
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thEsepRetzelsareMakingmetHirstythEsepRetzelsareMakingmetHirstythEs

Greg Wickham <greg@geelong.com> writes:
> 000528.19:45:45.725  [9553] query: SELECT  max( $1 ) FROM  $2

There is no facility in plpgsql for run-time specification of a table
name, and probably never will be for the general case.  It's possible
that it could be made to work for selection of a particular table among
the inheritance children of a specified table, but not for any arbitrary
table, unless we want to give up preparsing and preplanning of plpgsql
queries.

pltcl does everything on-the-fly at runtime, so you could do this in
that language, I think (and accept the resulting speed penalty).

A more interesting question is whether you shouldn't redesign your
database schema so that you don't need to do this...
        regards, tom lane