NotIn

NotIn is a concept used in programming to denote that an element is not a member of a collection. It appears as an operator or function in several languages, often written as not in or as a negated in clause.

In Python, the dedicated operator not in tests membership: x not in y evaluates to True when x is not contained in y. y can be any container implementing membership testing, such as lists, tuples, sets, dictionaries (as keys), or strings. The operation is equivalent to not (x in y).

In SQL, NOT IN filters rows whose value does not match any value in a list or subquery. For example: SELECT * FROM users WHERE status NOT IN ('inactive','banned'). Note that NULL values affect NOT IN results; if the list contains NULL, the result can be UNKNOWN rather than False, so NOT EXISTS is often used to handle NULLs reliably.

In Kotlin and some other languages, the negated form is built from in and !in: a !in collection means that a is not a member of collection. In JavaScript, in tests property existence (prop in obj); negation can be achieved with !(prop in obj).

NotIn semantics and performance vary by language. As a general rule, membership tests are faster for hash-based collections than for lists, and null handling can complicate NOT IN in SQL databases.