Arithmetic with distinct type operands

A distinct type cannot be used with arithmetic operators even if its source data type is numeric.

To perform an arithmetic operation, create a function with the arithmetic operator as its source. For example, if there were distinct types INCOME and EXPENSES, both of which had DECIMAL(8,2) data types, the following user-defined function, REVENUE, could be used to subtract one from the other.

  CREATE FUNCTION REVENUE ( INCOME, EXPENSES )
    RETURNS DECIMAL(8,2) SOURCE "-" ( DECIMAL, DECIMAL)

Alternately, the - (minus) operator could be overloaded using a function to subtract the new data types.

   CREATE FUNCTION "-" ( INCOME, EXPENSES )   
     RETURNS DECIMAL(8,2) SOURCE "-" ( DECIMAL, DECIMAL)

Alternatively, the distinct type can be cast to a built-in data type and the result used as an operand of an arithmetic operator.