PostgreSQL Operators

Comparison Operators

Comparison operators test the relationship between two values and always return a boolean result: true, false, or unknown (when NULL is involved). PostgreSQL supports the standard set: = for equality, <> or != for inequality, < and > for strictly less than or greater than, and <= and >= for inclusive bounds. These operators work on numbers, text, dates, and most other data types, comparing text using the current locale's collation rules.

• = tests equality between two values
• <> or != tests inequality (both are valid in PostgreSQL)
• < and > test strict ordering
• <= and >= test inclusive ordering
• Comparisons involving NULL always evaluate to unknown, not true or false

SELECT name, department, salary
FROM employees
WHERE salary > 50000;

Logical Operators

Logical operators combine multiple boolean expressions into a single condition. PostgreSQL implements the three standard logical operators: AND requires every condition to be true, OR requires at least one condition to be true, and NOT inverts a condition's truth value. These operators are most commonly used inside a WHERE clause to build precise multi-condition filters.

SELECT name, department
FROM employees
WHERE department = 'Engineering' AND salary > 70000;

SELECT name, department
FROM employees
WHERE (department = 'Sales' OR department = 'Marketing')
  AND commission IS NOT NULL;

Operator Precedence and NULL

When PostgreSQL evaluates an expression without explicit parentheses, comparison operators run first, NOT runs next, AND runs before OR. Relying on this default order makes queries harder to read and easy to get wrong, so most teams add parentheses around every logical grouping regardless of precedence rules.