Which select statement returns true?

Question

Options

• ASELECT NULL <> NULL;
• BSELECT NULL <=> NULL;
• CSELECT NULL = NULL;
• DSELECT NULL := NULL;

• A
  3% (1)
• B
  94% (32)
• C
  3% (1)

Explanation

Option B uses MySQL's NULL-safe equality operator (<=>), which is specifically designed to treat NULL <=> NULL as TRUE - unlike standard SQL operators, it handles NULL as a comparable value rather than an unknown.

Options A and C use standard comparison operators (<> and =), which always return NULL (not TRUE or FALSE) when either operand is NULL, because NULL represents an unknown value and any comparison with an unknown is itself unknown. Option D (NULL := NULL) uses the assignment operator, not a comparison operator at all - it assigns a value and doesn't return a boolean result in a SELECT context.

Memory tip: Think of <=> as the "spaceship operator" - it's built to bridge the gap that normal operators can't cross. If you see <=>, it's the only one that can safely land on NULL.

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