NULL Values: Missing Data Done Right

By Ravindra Bagale Last updated: 31 October 2026

Lessons in this chapter:

7.1 What NULL Means (Unknown — Not Zero, Not Blank Text)
7.2 How to Find Missing Values with IS NULL and IS NOT NULL
7.3 Why = NULL Never Works (Common Beginner Trap)
7.4 COALESCE and IFNULL to Fill a Display Value
7.5 COUNT(*) vs COUNT(column) When NULLs Exist
7.6 Practice: Missing Order Notes and Empty Ticket Fields

Quiz for this chapter is available on the Learn tracker after deploy.

Ravindra Bagale's Tip

Finish every lesson example in DB Browser before the quiz.

Ravi Sir's Cards for this chapter

NULL means missing. If you treat missing phone numbers like zero, your counts quietly go wrong.

Revision card How do you find rows where the phone number is missing? Use WHERE phone IS NULL. Writing = NULL does not work, because NULL is never equal to anything.

How do you find rows where the phone number is missing? Use WHERE phone IS NULL. Writing = NULL does not work, because NULL is never equal to anything.

Interview card NULL vs 0 vs empty text. NULL means unknown. 0 is a real number. Empty text '' is a text value with no letters in it.

Comparison card

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