Planning error in dynamic string creation in plpgsql

[Keith Fiske <keith@xxxxxxxxxx>]

Running into an issue trying to dynamically create some SQL statements in a plpgsql function. The function below is as simple an example I can make to reproduce the error. The first loop works without any issues, but the second throws an error.

CREATE OR REPLACE FUNCTION testing_record() RETURNS void
    LANGUAGE plpgsql
    AS $$
DECLARE
    v_col       text;
    v_col_names text[];
    v_record    record;
    v_sql       text;
BEGIN

CREATE TEMP TABLE test_temp (col1 int, col2 text, col3 timestamp);
INSERT INTO test_temp VALUES (1, 'stuff', now());
INSERT INTO test_temp VALUES (2, 'stuff', CURRENT_TIMESTAMP + '1 day'::interval);

v_col_names := '{"col1","col3"}';

FOR i IN 1..2
LOOP
    IF i = 1 THEN
        EXECUTE 'SELECT min(col1) as min, max(col1) as max FROM test_temp' INTO v_record;
        RAISE NOTICE 'v_record: %', v_record;
        v_sql := concat('col1 min: ', quote_literal(v_record.min), ', col1 max: ', quote_literal(v_record.max) );
        RAISE NOTICE 'v_sql: %', v_sql;
    ELSIF i = 2 THEN
        EXECUTE 'SELECT min(col3) as min, max(col3) as max FROM test_temp' INTO v_record;
        RAISE NOTICE 'v_record: %', v_record;
        v_sql := concat('col3 min: ', quote_literal(v_record.min), ', col3 max: ', quote_literal(v_record.max) );
        RAISE NOTICE 'v_sql: %', v_sql;
    END IF;
END LOOP;

FOREACH v_col IN ARRAY v_col_names
LOOP
       EXECUTE 'SELECT min('||v_col||') as min, max('||v_col||') as max FROM test_temp' INTO v_record;
       RAISE NOTICE 'v_record: %', v_record;
       v_sql := concat(v_col
            , ' min: '
            , quote_literal(v_record.min)
            , ', '
            , v_col
            , ' max: '
            , quote_literal(v_record.max)
          );
       RAISE NOTICE 'v_sql: %', v_sql;
END LOOP;

DROP TABLE IF EXISTS test_temp;

END
$$;

keith=# select testing_record();
NOTICE:  v_record: (1,2)
NOTICE:  v_sql: col1 min: '1', col1 max: '2'
NOTICE:  v_record: ("2014-01-05 21:24:21.039656","2014-01-06 21:24:21.039656")
NOTICE:  v_sql: col3 min: '2014-01-05 21:24:21.039656', col3 max: '2014-01-06 21:24:21.039656'
NOTICE:  v_record: (1,2)
NOTICE:  v_sql: col1 min: '1', col1 max: '2'
NOTICE:  v_record: ("2014-01-05 21:24:21.039656","2014-01-06 21:24:21.039656")
ERROR:  type of parameter 7 (timestamp without time zone) does not match that when preparing the plan (integer)
CONTEXT:  PL/pgSQL function testing_record() line 34 at assignment

I've narrowed down the exact point of the error being the quote_literal() calls. If I commend them out like this:

       v_sql := concat(v_col
            , ' min: '
--            , quote_literal(v_record.min)
            , ', '
            , v_col
            , ' max: '
--            , quote_literal(v_record.max)
          );
 

Then the function runs without any issues, but obviously the values are missing from the NOTICE

keith=# select testing_record();
NOTICE:  v_record: (1,2)
NOTICE:  v_sql: col1 min: '1', col1 max: '2'
NOTICE:  v_record: ("2014-01-05 21:25:58.603149","2014-01-06 21:25:58.603149")
NOTICE:  v_sql: col3 min: '2014-01-05 21:25:58.603149', col3 max: '2014-01-06 21:25:58.603149'
NOTICE:  v_record: (1,2)
NOTICE:  v_sql: col1 min: , col1 max:
NOTICE:  v_record: ("2014-01-05 21:25:58.603149","2014-01-06 21:25:58.603149")
NOTICE:  v_sql: col3 min: , col3 max:
 testing_record
----------------
 
(1 row)

In the real function I'm writing, the columns to be used in the string being created are pulled from a configuration table, so their types could be anything. So casting the quote_literal() calls is not really an option here.

Any help would be appreciated.

--
Keith Fiske
Database Administrator
OmniTI Computer Consulting, Inc.
http://www.keithf4.com