A composite-type, such as a table, or a user-defined type is passed to the PL/Tcl function as an associative array (Hash table). The attribute names of the composite-type are the element names in the array. Attributes with NULL values are not available in the Tcl array.

Let's take a look at an arbitrary example. We will create a function that takes a composite type as an argument and does some calculations based on the attribute values of the type. Let's create our type and the function:

CREATE TABLE orders(orderid int, num_people integer, order_amount decimal);

INSERT INTO orders VALUES(1,1,23);
INSERT INTO orders VALUES(2,3,157);
INSERT INTO orders VALUES(3,5,567.25);
INSERT INTO orders VALUES(4,1,100);

CREATE OR REPLACE FUNCTION tip_calculator(orders, integer) RETURNS decimal
AS $$
  if {$1(order_amount) > 0} {
    set tip [expr (double($1(order_amount) * $2)/100)/$1(num_people)]
    set tip [format "%.2f" $tip]
    return $tip
  }
  return 0;
$$ LANGUAGE...