Create dynamic table from function in PostgreSQL

Question

I have table data,

select * from tbltaxamount ;
 id |   taxname   | taxinfoid | taxvalue | taxamt | zoneid | invoiceid | transid 
----+-------------+-----------+----------+--------+--------+-----------+---------
  1 | Service Tax |         0 |     0.00 |  28.69 |      2 |       119 |      -1
  2 | ABC Tax     |         0 |     0.00 |  25.78 |      2 |       119 |      -1

Now, how can I get the result as below using any function of PostgreSQL?

invoiceid | Service Tax | ABC Tax
----------+-------------+--------
      119 |       28.69 |  25.78

Answer 1

Your solution is a viable way. I largely rewrote your plpgsql function for simplification / performance / readability / security.

CREATE OR REPLACE FUNCTION f_taxamount()
 RETURNS void AS
$BODY$
DECLARE
    rec record;
BEGIN

    DROP TABLE IF EXISTS tmptable;

    EXECUTE 'CREATE TABLE tmptable (invoiceid integer PRIMARY KEY, '
        || (
           SELECT string_agg(col || ' numeric(9,2) DEFAULT 0', ', ')
           FROM  (
              SELECT quote_ident(lower(replace(taxname,' ','_'))) AS col
              FROM   tbltaxamount
              GROUP  BY 1
              ORDER  BY 1
              ) x
           )
        || ')';

    EXECUTE '
        INSERT INTO tmptable (invoiceid)
        SELECT DISTINCT invoiceid FROM tbltaxamount';

    FOR rec IN
        SELECT taxname, taxamt, invoiceid FROM tbltaxamount ORDER BY invoiceid
    LOOP
        EXECUTE '
            UPDATE tmptable
            SET ' || quote_ident(lower(replace(rec.taxname,' ','_')))
                  || ' = '|| rec.taxamt || ' 
            WHERE invoiceid = ' || rec.invoiceid;
    END LOOP;

END;
$BODY$ LANGUAGE plpgsql;

This works for PostgreSQL 9.1 or later.

For pg 8.4 or later replace

SELECT string_agg(col || ' numeric(9,2) DEFAULT 0', ', ')

with:

SELECT array_to_string(array_agg(col || ' numeric(9,2) DEFAULT 0'), ', ')

For versions even older than that create an aggregate function like this:

CREATE OR REPLACE FUNCTION f_concat_comma(text, text)
  RETURNS text AS
$BODY$
BEGIN
RETURN ($1 || ', '::text) || $2;
END;
$BODY$
  LANGUAGE plpgsql IMMUTABLE;

CREATE AGGREGATE concat_comma(text) (
  SFUNC=f_concat_comma,
  STYPE=text
);

And then write:

SELECT concat_comma(col || ' numeric(9,2) DEFAULT 0')

---

Also:

DROP TABLE IF EXISTS tmptable;

The clause "IF EXISTS" was introduced with version 8.2.
If you should use a version even older than that you should you can:

IF EXISTS (
    SELECT *
    FROM   pg_catalog.pg_class
    WHERE  oid = 'tmptable'::regclass
    AND    relkind = 'r')
THEN
    DROP TABLE tmptable;
END IF;
*/

---

Upgrade!

Have a look at the versioning policy of the PostgreSQL project. Version 8.0.1 is an especially buggy version. I would strongly advise you to upgrade. If you can't upgrade to a newer major version, at least upgrade to the latest point-release for security reasons, 8.0.26 in your case. This can be done in place, without changing anything else.