Consider the following statements:

1. If all FieldName fields in the set are NULL, then aggregate functions return NULL in such cases.
2. The result of a relation algebra query can have duplicate records.
3. Relational calculus is a procedural query language, which takes instances of relations as input and yields instances of relations as output.
4. An SQL query can work without having any indexes on the relations.

Which of the following statement(s) is/are correct?
(A) Only 1, 3 and 4
(B) Only 1 and 4
(C) Only 2 and 3
(D) None of these


Answer: (D)

Explanation: If all FieldName fields in the set are NULL, then aggregate functions (except COUNT and COUNT(*)) return NULL in such cases.
The result of a relation algebra query will never have duplicate records.
Relational algebra is a procedural query language, which takes instances of relations as input and yields instances of relations as output.

Only statement 4 is correct.

So, option (D) is correct.

Quiz of this Question