GATE CS 2023 Q.61: SQL Queries and Integrity Constraints

Consider the following table named Student in a relational database. The primary key of this table is rollNum.

Student
rollNum	name	gender	marks
1	Naman	M	62
2	Aliya	F	70
3	Aliya	F	80
4	James	M	82
5	Swati	F	65

The SQL query below is executed on this database.

SELECT *
FROM Student
WHERE gender = 'F' AND marks > 65;

The number of rows returned by the query is _______.

Your answer

Official answer and solution

Solution

Evaluate the SQL WHERE predicate gender = 'F' AND marks > 65 against each row of table Student.

Evaluating each tuple in the Student table:

(1, Naman, M, 62): gender = 'M' $\implies$ FALSE.
(2, Aliya, F, 70): gender = 'F' (TRUE) and marks = 70 > 65 (TRUE) $\implies$ Selected.
(3, Aliya, F, 80): gender = 'F' (TRUE) and marks = 80 > 65 (TRUE) $\implies$ Selected.
(4, James, M, 82): gender = 'M' $\implies$ FALSE.
(5, Swati, F, 65): gender = 'F' (TRUE) but marks = 65 > 65 is FALSE (strict inequality) $\implies$ NOT selected.

Exactly 2 rows satisfy the WHERE condition.

Final answer

Common trap

Including Swati whose marks are exactly 65 (the condition uses strict inequality > 65).

The answer is the one in the official GATE answer key. The solution is this site's own explanation.

GATE questions are the work of the organising institutes. This site is independent and is not affiliated with them.