Programming · Flashcard
What does the comparison price = NULL evaluate to?
- AUnknown — comparisons with NULL are never true, so the row is filtered out
- BTrue for NULL prices — equality is the standard way to test for missing values
- CFalse for every row — the parser rewrites the comparison to a constant
- DA syntax error — NULL is a keyword and cannot appear after an operator
Why this is the answer
Any comparison with NULL yields unknown (three-valued logic), and WHERE keeps only true rows — so = NULL matches nothing, even NULL prices. It's not the correct test (that's IS NULL), not a constant-false rewrite, and it parses fine.
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