24 NULL Handling questions from the SQL bank, written for Indian campus drives and tech interviews. Every question has a verified answer and an AI-tutor explanation on placd.
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A.the behavior whereby functions like SUM, AVG, and COUNT(column) silently ignore rows whose value is absent, while COUNT(*) still counts them
B.a function returning the first non-missing value from its argument list, often used to substitute a default when a column has no value
C.a marker representing a missing or unknown value rather than zero or an empty string
D.a function returning the missing-value marker when its two arguments are equal and otherwise returning the first argument
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2. Which term means: "a marker representing a missing or unknown value rather than zero or an empty string"?
Junior
A.NULL
B.aggregate NULL skipping
C.COALESCE
D.IS NULL
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3. Which statement is correct?
Junior
A.NULL — the rule that GROUP BY and DISTINCT treat all missing-value markers as equal and collapse them into a single group, contrary to ordinary equality
B.NULL — a marker representing a missing or unknown value rather than zero or an empty string
C.NULL — the behavior whereby functions like SUM, AVG, and COUNT(column) silently ignore rows whose value is absent, while COUNT(*) still counts them
D.NULL — the system in which a predicate may yield true, false, or unknown, so comparisons involving a missing value produce neither true nor false
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4. What is IS NULL?
Junior
A.the system in which a predicate may yield true, false, or unknown, so comparisons involving a missing value produce neither true nor false
B.a function returning the first non-missing value from its argument list, often used to substitute a default when a column has no value
C.a function returning the missing-value marker when its two arguments are equal and otherwise returning the first argument
D.the correct predicate for testing the absence of a value, since a normal equality comparison against the missing-value marker never evaluates to true
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5. Which term means: "the correct predicate for testing the absence of a value, since a normal equality comparison against the missing-value marker never evaluates to true"?
Junior
A.aggregate NULL skipping
B.three-valued logic
C.NULLIF
D.IS NULL
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6. Which statement is correct?
Junior
A.IS NULL — an ordering option controlling whether rows with a missing value sort before or after real values, since their default position varies by engine
B.IS NULL — a function returning the missing-value marker when its two arguments are equal and otherwise returning the first argument
C.IS NULL — the correct predicate for testing the absence of a value, since a normal equality comparison against the missing-value marker never evaluates to true
D.IS NULL — the system in which a predicate may yield true, false, or unknown, so comparisons involving a missing value produce neither true nor false
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7. What is three-valued logic?
Mid
A.the system in which a predicate may yield true, false, or unknown, so comparisons involving a missing value produce neither true nor false
B.the behavior whereby functions like SUM, AVG, and COUNT(column) silently ignore rows whose value is absent, while COUNT(*) still counts them
C.the correct predicate for testing the absence of a value, since a normal equality comparison against the missing-value marker never evaluates to true
D.a function returning the missing-value marker when its two arguments are equal and otherwise returning the first argument
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8. Which term means: "the system in which a predicate may yield true, false, or unknown, so comparisons involving a missing value produce neither true nor false"?
Mid
A.aggregate NULL skipping
B.NULL
C.IS NULL
D.three-valued logic
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9. Which statement is correct?
Mid
A.three-valued logic — the system in which a predicate may yield true, false, or unknown, so comparisons involving a missing value produce neither true nor false
B.three-valued logic — an ordering option controlling whether rows with a missing value sort before or after real values, since their default position varies by engine
C.three-valued logic — the behavior whereby functions like SUM, AVG, and COUNT(column) silently ignore rows whose value is absent, while COUNT(*) still counts them
D.three-valued logic — a function returning the missing-value marker when its two arguments are equal and otherwise returning the first argument
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10. What is COALESCE?
Junior
A.the correct predicate for testing the absence of a value, since a normal equality comparison against the missing-value marker never evaluates to true
B.the rule that GROUP BY and DISTINCT treat all missing-value markers as equal and collapse them into a single group, contrary to ordinary equality
C.the system in which a predicate may yield true, false, or unknown, so comparisons involving a missing value produce neither true nor false
D.a function returning the first non-missing value from its argument list, often used to substitute a default when a column has no value
Answer + AI explanation with Pro
11. Which term means: "a function returning the first non-missing value from its argument list, often used to substitute a default when a column has no value"?
Junior
A.NULLIF
B.COALESCE
C.NULL
D.NULLS FIRST
Answer + AI explanation with Pro
12. Which statement is correct?
Junior
A.COALESCE — an ordering option controlling whether rows with a missing value sort before or after real values, since their default position varies by engine
B.COALESCE — a function returning the first non-missing value from its argument list, often used to substitute a default when a column has no value
C.COALESCE — a function returning the missing-value marker when its two arguments are equal and otherwise returning the first argument
D.COALESCE — a marker representing a missing or unknown value rather than zero or an empty string
Answer + AI explanation with Pro
13. What is NULLIF?
Mid
A.the behavior whereby functions like SUM, AVG, and COUNT(column) silently ignore rows whose value is absent, while COUNT(*) still counts them
B.a function returning the missing-value marker when its two arguments are equal and otherwise returning the first argument
C.the correct predicate for testing the absence of a value, since a normal equality comparison against the missing-value marker never evaluates to true
D.a marker representing a missing or unknown value rather than zero or an empty string
Answer + AI explanation with Pro
14. Which term means: "a function returning the missing-value marker when its two arguments are equal and otherwise returning the first argument"?
Mid
A.NULL grouping equivalence
B.COALESCE
C.IS NULL
D.NULLIF
Answer + AI explanation with Pro
15. Which statement is correct?
Mid
A.NULLIF — the behavior whereby functions like SUM, AVG, and COUNT(column) silently ignore rows whose value is absent, while COUNT(*) still counts them
B.NULLIF — a function returning the missing-value marker when its two arguments are equal and otherwise returning the first argument
C.NULLIF — the correct predicate for testing the absence of a value, since a normal equality comparison against the missing-value marker never evaluates to true
D.NULLIF — the rule that GROUP BY and DISTINCT treat all missing-value markers as equal and collapse them into a single group, contrary to ordinary equality
Answer + AI explanation with Pro
16. What is aggregate NULL skipping?
Mid
A.the behavior whereby functions like SUM, AVG, and COUNT(column) silently ignore rows whose value is absent, while COUNT(*) still counts them
B.the correct predicate for testing the absence of a value, since a normal equality comparison against the missing-value marker never evaluates to true
C.the system in which a predicate may yield true, false, or unknown, so comparisons involving a missing value produce neither true nor false
D.a function returning the first non-missing value from its argument list, often used to substitute a default when a column has no value
Answer + AI explanation with Pro
17. Which term means: "the behavior whereby functions like SUM, AVG, and COUNT(column) silently ignore rows whose value is absent, while COUNT(*) still counts them"?
Mid
A.aggregate NULL skipping
B.NULL
C.NULLS FIRST
D.NULL grouping equivalence
Answer + AI explanation with Pro
18. Which statement is correct?
Mid
A.aggregate NULL skipping — the behavior whereby functions like SUM, AVG, and COUNT(column) silently ignore rows whose value is absent, while COUNT(*) still counts them
B.aggregate NULL skipping — a function returning the missing-value marker when its two arguments are equal and otherwise returning the first argument
C.aggregate NULL skipping — a function returning the first non-missing value from its argument list, often used to substitute a default when a column has no value
D.aggregate NULL skipping — a marker representing a missing or unknown value rather than zero or an empty string
Answer + AI explanation with Pro
19. What is NULL grouping equivalence?
Senior
A.an ordering option controlling whether rows with a missing value sort before or after real values, since their default position varies by engine
B.a function returning the missing-value marker when its two arguments are equal and otherwise returning the first argument
C.the rule that GROUP BY and DISTINCT treat all missing-value markers as equal and collapse them into a single group, contrary to ordinary equality
D.the correct predicate for testing the absence of a value, since a normal equality comparison against the missing-value marker never evaluates to true
Answer + AI explanation with Pro
20. Which term means: "the rule that GROUP BY and DISTINCT treat all missing-value markers as equal and collapse them into a single group, contrary to ordinary equality"?
Senior
A.NULL
B.NULL grouping equivalence
C.NULLS FIRST
D.aggregate NULL skipping
Answer + AI explanation with Pro
21. Which statement is correct?
Senior
A.NULL grouping equivalence — the behavior whereby functions like SUM, AVG, and COUNT(column) silently ignore rows whose value is absent, while COUNT(*) still counts them
B.NULL grouping equivalence — a marker representing a missing or unknown value rather than zero or an empty string
C.NULL grouping equivalence — the correct predicate for testing the absence of a value, since a normal equality comparison against the missing-value marker never evaluates to true
D.NULL grouping equivalence — the rule that GROUP BY and DISTINCT treat all missing-value markers as equal and collapse them into a single group, contrary to ordinary equality
Answer + AI explanation with Pro
22. What is NULLS FIRST?
Senior
A.a function returning the first non-missing value from its argument list, often used to substitute a default when a column has no value
B.the rule that GROUP BY and DISTINCT treat all missing-value markers as equal and collapse them into a single group, contrary to ordinary equality
C.a marker representing a missing or unknown value rather than zero or an empty string
D.an ordering option controlling whether rows with a missing value sort before or after real values, since their default position varies by engine
Answer + AI explanation with Pro
23. Which term means: "an ordering option controlling whether rows with a missing value sort before or after real values, since their default position varies by engine"?
Senior
A.NULL
B.IS NULL
C.NULLIF
D.NULLS FIRST
Answer + AI explanation with Pro
24. Which statement is correct?
Senior
A.NULLS FIRST — an ordering option controlling whether rows with a missing value sort before or after real values, since their default position varies by engine
B.NULLS FIRST — a function returning the missing-value marker when its two arguments are equal and otherwise returning the first argument
C.NULLS FIRST — the rule that GROUP BY and DISTINCT treat all missing-value markers as equal and collapse them into a single group, contrary to ordinary equality
D.NULLS FIRST — the behavior whereby functions like SUM, AVG, and COUNT(column) silently ignore rows whose value is absent, while COUNT(*) still counts them
Answer + AI explanation with Pro
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