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NULL Values: Missing Data Done Right — Ravi Sir's Cards

All SQL cards

Revision cards

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

Interview cards

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? · PNG

Comparison cards

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.
NULL vs 0 vs empty text · PNG