When you write a new version of an operator function,
follow these rules:
The name of the operator function must match the name of an
arithmetic, text, or relational-operator function. The name is case
insensitive; the plus() function is the same
as the Plus() function.
The operator function must handle the correct number of parameters.
The operator function must return the correct data type.
Tip:
Although the compare() function is
not strictly an operator function, when you overload the relational
operators, you should prepare a corresponding compare() function,
because the database server uses compare() to
process queries that SELECT DISTINCT or
have an ORDER BY clause.
If you define a compare() function, you
must also define the greaterthan(), lessthan(),
or other functions that use the compare function.