24 real NULL Handling questions from the SQL bank, as asked in Indian campus drives and tech interviews. Every question has a verified answer and an AI-tutor explanation on placd — free to start.
1. What is NULL?
Junior
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
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
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
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"?
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
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
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"?
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
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
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"?
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
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
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
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
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"?
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
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
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"?
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
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"?
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
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