Notequal

Notequal, or not-equal, denotes the binary relation that two values are different. In mathematics it is expressed by the symbol ≠ and is used to indicate that two numbers, expressions, or objects do not represent the same quantity.

In computing, the not-equal relation is an operator or predicate that compares two operands and yields a boolean result: true if they differ, false if they are the same. It appears in many languages with textual forms such as != or <>, and in SQL and some languages both forms are accepted. The exact behavior can vary by language, particularly regarding type handling and coercion.

Semantics vary by language. Some languages apply type conversion before comparison (loose inequality), while others require comparable types or provide separate strict operators. For example, JavaScript treats != with type coercion, while !== performs strict comparison without coercion. In SQL, comparisons behave according to three-valued logic: if either side is NULL, the result is UNKNOWN rather than true or false; many dialects also support <> and !=, and some offer IS DISTINCT FROM to handle NULL semantics more predictably.

Edge cases follow platform conventions. In floating-point arithmetic, IEEE 754 defines that NaN is not equal to any value, including itself, so NaN != NaN is true in most environments. In pure mathematics, the notion of equality is well-defined for real numbers, and not-equal simply asserts inequality without the complications of special values.

See also: equality, inequality, relational operators.