Understanding Operators in PostgreSQL

Introduction

PostgreSQL is a powerful and popular relational database management system that supports a large number of data types, functions, and operators. Operators are special symbols or keywords that perform some operation on one or more operands and produce a result. For example, the operator + performs addition on two numeric operands and returns their sum.

Operators are often used in the WHERE clause of SQL statements to specify conditions for filtering data. For example, the following query returns all the records from the cars table where the brand column is equal to 'Volvo':

SELECT * FROM cars WHERE brand = 'Volvo';

The operator = is used to check for equality between two values. PostgreSQL supports many other operators for different purposes, such as comparison, arithmetic, logical, pattern matching, and more. In this article, we will explore some of the most common and useful operators in PostgreSQL and how to use them.

Comparison Operators in PostgreSQL

Comparison operators are used to compare two values and return a boolean value (true, false, or null) as the result. Comparison operators can be used with any data type that supports ordering, such as numbers, strings, dates, and enums. The following table lists the comparison operators in PostgreSQL:

Operator	Description	Example
=	Equal to	brand = 'Volvo'
<> or !=	Not equal to	brand <> 'Volvo'
<	Less than	model < 1975
>	Greater than	model > 1975
<=	Less than or equal to	model <= 1975
>=	Greater than or equal to	model >= 1975

Note that the comparison operators are case sensitive, meaning that 'Volvo' and 'volvo' are not considered equal. To perform case insensitive comparison, you can use the ILIKE operator, which we will discuss later.

Arithmetic Operators in PostgreSQL

Arithmetic operators are used to perform mathematical operations on numeric operands and return a numeric result. Arithmetic operators can be used with any data type that supports arithmetic, such as integers, floats, decimals, and intervals. The following table lists the arithmetic operators in PostgreSQL:

Operator	Description	Example
+	Addition	price + 1000
-	Subtraction	price - 1000
*	Multiplication	price * 1.1
/	Division	price / 2
%	Modulo (remainder)	price % 100
^	Exponentiation	price ^ 2

Note that the arithmetic operators follow the standard order of precedence, meaning that exponentiation is performed first, followed by multiplication, division, and modulo, and then addition and subtraction. You can use parentheses to change the order of evaluation, such as (price + 1000) / 2.

Logical Operators in PostgreSQL

Logical operators are used to combine two or more boolean values and return a boolean result. Logical operators can be used with any data type that can be cast to boolean, such as numbers, strings, and nulls. The following table lists the logical operators in PostgreSQL:

Operator	Description	Example
AND	Logical AND (returns true if both operands are true)	brand = 'Volvo' AND model > 1975
OR	Logical OR (returns true if either operand is true)	brand = 'Volvo' OR brand = 'BMW'
NOT	Logical NOT (returns the opposite of the operand)	NOT (brand = 'Volvo')

Note that the logical operators follow the standard order of precedence, meaning that NOT is performed first, followed by AND, and then OR. You can use parentheses to change the order of evaluation, such as (brand = 'Volvo' OR brand = 'BMW') AND model > 1975.

Pattern Matching Operators in PostgreSQL

Pattern matching operators are used to check if a value matches a certain pattern, such as a substring, a regular expression, or a wildcard. Pattern matching operators are mainly used with string data types, such as text, varchar, and char. The following table lists the pattern matching operators in PostgreSQL:

Operator	Description	Example
LIKE	Matches a value with a pattern using the % and _ wildcards (case sensitive)	brand LIKE 'V%'
ILIKE	Matches a value with a pattern using the % and _ wildcards (case insensitive)	brand ILIKE 'v%'
SIMILAR TO	Matches a value with a pattern using the SQL standard regular expression syntax (case sensitive)	brand SIMILAR TO 'V[A-Z]%'
~	Matches a value with a pattern using the POSIX regular expression syntax (case sensitive)	brand ~ '^V[A-Z]'
~*	Matches a value with a pattern using the POSIX regular expression syntax (case insensitive)	brand ~* '^v[a-z]'

The % wildcard matches any sequence of zero or more characters, while the _ wildcard matches any single character. For example, the pattern 'V%' matches any value that starts with a capital 'V', such as 'Volvo', 'Volkswagen', and 'Viper'. The pattern 'V_o%' matches any value that starts with a capital 'V', followed by any character, followed by a lowercase 'o', such as 'Volvo' and 'Voodoo'.

The SIMILAR TO operator uses the SQL standard regular expression syntax, which is similar to the POSIX syntax, but with some differences. For example, the pattern 'V[A-Z]%' matches any value that starts with a capital 'V', followed by any capital letter, followed by any sequence of characters, such as 'Volvo' and 'VW'. The pattern 'V_[A-Z]%' matches any value that starts with a capital 'V', followed by any character, followed by a capital letter, followed by any sequence of characters, such as 'V8' and 'VX4'.

The ~ and ~* operators use the POSIX regular expression syntax, which is more powerful and flexible than the SQL standard syntax. For example, the pattern '^V[A-Z]' matches any value that starts with a capital 'V', followed by any capital letter, such as 'Volvo' and 'VW'. The pattern '^V.[A-Z]' matches any value that starts with a capital 'V', followed by any character, followed by a capital letter, such as 'V8' and 'VX4'. The ^ symbol matches the beginning of the value, while the . symbol matches any single character.

Note that the pattern matching operators are case sensitive, except for ILIKE and ~*, which are case insensitive. To perform case insensitive matching with the other operators, you can use the LOWER or UPPER functions to convert the values to lower or upper case before comparing them. For example, LOWER(brand) LIKE 'v%'.

Other Operators

PostgreSQL also supports many other operators for specific data types, such as arrays, ranges, JSON, XML, geometric, network, and more. These operators provide various functionalities, such as indexing, concatenation, containment, overlap, intersection, and more. For example, the following query returns all the records from the cars table where the features column, which is an array of text, contains the value 'sunroof':

SELECT * FROM cars WHERE 'sunroof' = ANY (features);

The ANY operator checks if the value 'sunroof' is equal to any element of the array features. Similarly, the following query returns all the records from the cars table where the price column, which is a range of numeric values, overlaps with the range [10000, 20000]:

SELECT * FROM cars WHERE price && NUMRANGE(10000, 20000);

The && operator checks if the range price overlaps with the range NUMRANGE(10000, 20000), meaning that they have at least one value in common.

Conclusion

In this article, we have learned about some of the most common and useful operators in PostgreSQL and how to use them. Operators are essential tools for performing various operations on data and specifying conditions for filtering data. PostgreSQL supports a large number of operators for different data types, functions, and purposes. By understanding and using the operators in PostgreSQL, you can write more powerful and efficient SQL queries and manipulate data more easily.