isNot

isNot is a term used in programming to describe the negated form of the identity-checking operator, or, in SQL contexts, the negation of the IS predicate. In many languages, the basic operator is is, which tests whether two references point to the exact same object (identity) rather than whether their values are equal. The negated form is written as is not or isNot in documentation and code samples, and it yields true when the operands do not refer to the same object.

In Python, is and is not compare identity. They are distinct from value equality operators, == and !=. They are commonly used to test against None: x is None and x is not None. For example, two separate lists with identical content may be equal (a == b) but are not identical (a is not b), even though both lists contain the same elements.

In SQL, IS NOT is a binary predicate used for NULL checks and certain boolean comparisons. For example, value IS NOT NULL returns rows where value has a non-null entry, while column IS NOT TRUE checks for values that are not true. The IS/IS NOT predicates differ from typical inequality operators used for numeric or string comparisons.

Other languages may implement negation of a comparison with different syntax, such as not in front of a standard comparison (not a > b), or use != or <> for value inequality. Users should distinguish between identity-based negation (is not) and value-based inequality, and be aware that using is not for general inequality may lead to logical errors if identity semantics are mistaken for equality semantics.