IS NULL and IS NOT NULL

What is NULL?

Examples

-- find students with no phone number
SELECT * FROM students WHERE phone IS NULL;

-- find students who have a phone number
SELECT * FROM students WHERE phone IS NOT NULL;

Common Trap

Summary

• NULL = unknown/missing, not 0 or empty.
• Test with IS NULL / IS NOT NULL, never = NULL.

NULL क्या है?

Examples

-- बिना phone वाले students
SELECT * FROM students WHERE phone IS NULL;

-- जिनके पास phone है
SELECT * FROM students WHERE phone IS NOT NULL;

Common Trap

सारांश

• NULL = अज्ञात/missing, 0 या empty नहीं।
• IS NULL / IS NOT NULL से test करें, कभी = NULL नहीं।