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Databases - Practical PostgreSQL
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Chapter 5. Operators and Functions

Table of Contents
Operators
Functions

This chapter expands on the operators and functions available to PostgreSQL. These character symbols and identifiers allow you to flexibly modify and compare results within SQL statements. The results of these operations can be used in a variety of ways, from updating existing row data, to constraining query results to only rows matching particular conditions.

PostgreSQL supports the usual variety of standard SQL operators and functions as defined by the ANSI/ISO SQL standards, such as mathematical operators, basic text formatting functions, and date and time value extraction. PostgreSQL also comes with a rich set of custom PostgreSQL extensions, such as regular expression comparison operators, and the flexible to_char() text conversion function.

Take note that these sections describe the native operators and functions available to PostgreSQL. An excellent feature of PostgreSQL is its extensibility in this area. Once you have a solid understanding of operators and functions, you may be interested in developing your own. These techniques are described in Chapter 7.

Operators

In Chapter 3, operators are defined syntactically as tokens that are used to perform operations on values (e.g., constants, or identifiers), and return the results of that operation. In addition to these syntactic character symbols, there are some SQL keywords that are considered operators due to their effect on values in a SQL statement. Throughout this section, both these symbols and keywords will be referred to as operators.

The function of each operator is highly dependent on its context. Applications of operators range from performing mathematical operations and concatenating character strings, to performing a wide variety of comparisons yielding Boolean results. This section describes the general usage of operators in SQL, with successive sections on the following families of operators:

  • Character string

  • Numeric

  • Logical

Note: For an up-to-date and complete list of PostgreSQL supported operators, you can use psql  's \do slash command to view a list of available operators. Understand that many of the listed operators are PostgreSQL-specific, and therefore may not exist in other SQL-capable databases implementations.

Following the discussions of the various types of operators, you'll find information on dealing with NULL values in expressions, and on the order in which operators are evaluated.

Databases - Practical PostgreSQL
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