NULL represents a missing, unknown, or unavailable value in SQL. NULL is not the same as zero, an empty string, or a blank value. Because NULL represents the absence of a known value, it must be handled using special SQL conditions such as IS NULL and IS NOT NULL rather than normal equality comparisons.
Real-world datasets often contain missing information. Analysts must understand NULL correctly to avoid incorrect calculations, filtering problems, and misleading reports.
An employee record may not contain a LeavingDate because the employee is still working for the company. The LeavingDate can therefore contain NULL.
SELECT
EmployeeName,
Department
FROM Employees
WHERE ManagerID IS NULL;NULL values are common in customer records, employee data, financial transactions, product information, survey datasets, and operational databases.
- NULL represents a missing or unknown value.
- NULL is not the same as zero.
- NULL is not the same as an empty string.
- IS NULL is used to find NULL values.
- IS NOT NULL is used to find available values.
What does NULL mean in SQL?
NULL represents a missing, unknown, or unavailable value.
Can you use = NULL in SQL?
Normally no. IS NULL should be used to check whether a value is NULL.