Postgres Dynamic Query Function

Question

I need to create a function that will run a query and return the results with the table name and the column name being arugments given to the function. I currently have this:

CREATE OR REPLACE FUNCTION qa_scf(tname character varying, cname character varying)
RETURNS SETOF INT AS
$BODY$
BEGIN
RETURN QUERY SELECT * FROM tname WHERE cname !='AK' AND cname!='CK';
END;
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100
ROWS 1000;

This gives me the error "Relation 'tname' des not exist" when run. I'm new to function creating for Postgres, so any help is appreciated. I feel like the return int is wrong, but I don't know what else to put to make it return all columns for the rows returned. Thanks!

Answer 1

You cannot use a variable in place of an identifier like that. You need to do it with dynamic queries. It will look something like this:

EXECUTE 'SELECT * FROM ' || quote_ident(tname) 
        || ' WHERE ' || quote_ident(cname) || ' NOT IN (''AK'',''CK'');'
INTO result_var;

If you are using PostgreSQL 9.1 or above, you can use the format() function which makes constructing this string much easier.

Answer 2

Table and column names can not be specified as parameters or variables without dynamically constructing a string to execute as a dynamic statement. Postgres has excellent introductory documentation about executing dynamic statements . It's important to properly quote identifiers and literals with quote_ident() or quote_literal() . The format() function helps clean up dynamic sql statement construction. Since you declare the function to return SETOF INTEGER , you should select the integer field you want, not * .

CREATE OR REPLACE FUNCTION qa_scf(tname text, cname text)
RETURNS SETOF INTEGER AS
$BODY$
BEGIN
  RETURN QUERY EXECUTE format(
    'SELECT the_integer_field FROM %I WHERE %I NOT IN (%L,  %L)',
                                   tname,   cname,    'AK', 'CK'
  );
END;
$BODY$
LANGUAGE plpgsql;