IS operator in SQL?

The IS operator is used only to compare with NULL.

In SQL:

• = cannot be used to check NULL
• NULL means unknown / missing value
• So you must use:

✔ IS NULL

To check if a value is NULL

✔ IS NOT NULL

To check if a value is NOT NULL

✅ Why can't we use = with NULL?

NULL = NULL is not true.

SQL treats NULL as unknown, not a value.

That's why:

❌ WHERE allergy = NULL → wrong

✔ WHERE allergy IS NULL → correc

✅ LIKE Operator

Used to search for a pattern in text.