PostgreSQL supports left unary,
right unary, and binary
operators. Operators can be overloaded; that is,
the same operator name can be used for different operators
that have different numbers and types of operands. If
there is an ambiguous situation and the system cannot
determine the correct operator to use, it will return
an error. You may have to type-cast the left and/or
right operands to help it understand which operator you
meant to use.
Every operator is "syntactic sugar" for a call to an
underlying function that does the real work; so you must
first create the underlying function before you can create
the operator. However, an operator is not merely
syntactic sugar, because it carries additional information
that helps the query planner optimize queries that use the
operator. Much of this chapter will be devoted to explaining
that additional information.
