SQL Interview Question #9 | What is NULL in SQL?

SQL Interview Question #9

What is NULL in SQL?

NULL represents missing, unknown, or unavailable data.

❌ NULL is not 0

❌ NULL is not an empty string

✅ NULL means no value exists

Example:

An employee has not provided an email address yet.

Email = NULL

Filtering NULL Values:

To find NULL values:

SELECT * FROM Employees
WHERE Email IS NULL;

To find non-NULL values:

SELECT * FROM Employees
WHERE Email IS NOT NULL;

💡 Daily Use Case:

In real-world applications, fields like Email, Phone Number, Middle Name, or Address may contain NULL values when the information is not available.

💡 Interview Tip:

Never use = NULL

Always use IS NULL or IS NOT NULL

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