Practical PostgreSQL

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 those operations. 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.

Using Operators

Operators operate on either a single value or a pair of values. The majority ...