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Chapter 14. Extending SQL: Operators

Table of Contents
14.1. Introduction
14.2. Example
14.3. Operator Optimization Information
14.3.1. COMMUTATOR
14.3.2. NEGATOR
14.3.3. RESTRICT
14.3.4. JOIN
14.3.5. HASHES
14.3.6. SORT1 and SORT2

14.1. Introduction

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.

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