How to round REAL type to NUMERIC?

Question

I have table with real column type with example values:

123456,12
0,12345678

And code in stored procedure:

CREATE          


        

Answer 1

real is a lossy, inexact floating-point type. It only uses 4 bytes for storage and cannot store the presented numeric literals precisely to begin with. In addition, implementation details depend on your platform. Consider the chapter "Floating-Point Types" in the manual.

There is nothing wrong with either round() or cast(). For exact results, you'd have to use numeric to begin with.

Function audit

CREATE OR REPLACE FUNCTION test3()
  RETURNS void AS
$func$
DECLARE
   r record;
BEGIN
   FOR r IN 
      SELECT abs_km AS km
            ,cast(abs_km AS numeric) AS km_cast
            ,round(abs_km::numeric, 2) AS km_round
      FROM   gps_entry
   LOOP
      RAISE NOTICE 'km: % , km_cast: % , km_round: %'
                  , r.km, r.km_cast, r.km_round;
      INSERT INTO test (km, casting, rounding)
      VALUES (r.km, r.km_cast, r.km_round);
   END LOOP;    
END
$func$ LANGUAGE plpgsql;

• Do not quote the language name plpgsql. It's an identifier.

• Makes no sense to round to 2 fractional digits after casting to numeric(16,2), which forcibly rounds already. Either - or ..

  round(abs_km:: numeric(16,2), 2) as round
  round(abs_km::numeric, 2) as round
  abs_km::numeric(16,2) as round

Finally, you need to upgrade to a current version. Postgres 8.3 has reached EOL and is unsupported.