Here is an example of creating an operator for adding two complex
numbers. We assume we've already created the definition of type
complex (see Chapter 10). First we need a
function that does the work, then we can define the operator:
CREATE FUNCTION complex_add(complex, complex)
RETURNS complex
AS 'PGROOT/tutorial/complex'
LANGUAGE C;
CREATE OPERATOR + (
leftarg = complex,
rightarg = complex,
procedure = complex_add,
commutator = +
);
Now we can do:
SELECT (a + b) AS c FROM test_complex;
c
-----------------
(5.2,6.05)
(133.42,144.95)
We've shown how to create a binary operator here. To create unary
operators, just omit one of leftarg (for left unary) or
rightarg (for right unary). The procedure
clause and the argument clauses are the only required items in
CREATE OPERATOR. The commutator
clause shown in the example is an optional hint to the query
optimizer. Further details about commutator and other
optimizer hints appear below.
