SQL NOT Operator

NOT reverses a condition — it returns rows where the condition is false.

Syntax

WHERE NOT condition

Sample Table: employees

Example

SELECT name FROM employees
WHERE NOT department = 'Engineering';

Equivalent, and usually more readable:

SELECT name FROM employees
WHERE department <> 'Engineering';

Output: Riya, Neha.

NOT with IN, BETWEEN, LIKE, IS NULL

WHERE department NOT IN ('Engineering', 'Design')
WHERE salary NOT BETWEEN 50000 AND 70000
WHERE name NOT LIKE 'A%'
WHERE manager_id IS NOT NULL

These forms are usually clearer than wrapping the whole expression in NOT (...).

Practical Use Case

Excluding a specific set of rows is often easier to express with NOT than by listing every value you do want — e.g. "every department except Engineering" is one condition instead of enumerating the rest.

Common Mistakes

• NOT and NULL don't mix the way people expect. WHERE NOT department = 'Engineering' will silently exclude rows where department is NULL — NULL never satisfies = or its negation. If you need NULLs included, handle them explicitly.
• Writing deeply nested NOT (A AND NOT B) logic instead of simplifying it first — hard to read and easy to get wrong

Interview Relevance

Q: "Does WHERE NOT department = 'Engineering' return rows where department is NULL?" No — and explaining why (three-valued logic: NULL comparisons return UNKNOWN, not TRUE) is a strong signal in an interview.

Practice Question

Write a query for all employees NOT in the "Design" or "Marketing" departments, using NOT IN.

Related SQL Notes

• AND / OR
• IN
• IS NULL