CREATE TABLE mytable (id SERIAL, name VARCHAR(10) PRIMARY KEY)

INSERT INTO mytable (name) VALUES ('Jonas') RETURNING id

CREATE OR REPLACE FUNCTION upsert_tableName(arg1 type, arg2 type) RETURNS VOID AS $$
DECLARE
BEGIN
    UPDATE tableName SET col1 = value WHERE colX = arg1 and colY = arg2;
    IF NOT FOUND THEN
    INSERT INTO tableName values (value, arg1, arg2);
    END IF;
END;
$$ LANGUAGE 'plpgsql';

BEGIN
    INSERT INTO db_table (tbl_column) VALUES (v_tbl_column);
  EXCEPTION WHEN unique_violation THEN
    -- Ignore duplicate inserts.
  END;