Question
In a relational database, which key uniquely identifies
tuples within a table and can never contain NULL values?Solution
A Primary Key uniquely identifies each record (or tuple) in a table and cannot contain NULL values. It enforces entity integrity, ensuring that every row in a table has a unique identifier. For example, in a table of employees, an employee ID serves as a primary key, ensuring no duplicate or NULL entries exist. Why Other Options Are Incorrect:
- Foreign Key: Links one table to another and can contain NULL values in some cases; its purpose is to enforce referential integrity, not uniqueness within its table.
- Candidate Key: A potential key that can uniquely identify tuples but is not chosen as the primary key.
- Alternate Key: A candidate key not selected as the primary key but still capable of uniquely identifying records.
- Composite Key: A primary key consisting of multiple columns but is a type of primary key, not a separate concept.
Statements: Z > Y ≥ X; I < N ≤ L; F < I > D > Z
Conclusions:
I. L > F
II. X < N
III. Y < I
Which of the following expression symbols should replace the question mark(?) in the given expressions to make the expression C ≥ E as well as D > M d...
Statement: C > S > F > B > L; I > B > T
Conclusion: I. I > L II. T < C
Statement: J ≥ K ≥ L = M ≤ N = O
Conclusions:
I. J > N
II. L ≤ OWhich of the following is true in the given expression?
 G < H ≤ I, V ≥ W = G, R ≤ I = A
In the following question the relationship between different elements is given in the statements followed by two conclusions I and II. Read the stateme...
Statements: Q > R ≥ L = O ≤ M > S = T ≤ N
Conclusion
I: N ≤ L
II: N > L
Statements: M > P > Q < R = T; A < B ≤ C = P; L > N = T > X
Conclusions:
I. Â R > P
II. Â R < P
...Statements:
L ≤ J ≤ C = N; W ≥ X > L
Conclusions:
I. J ≤ X
II. X ˃ W
Statement: F ≥ G > I > E ≤ P, E = S ≥ PÂ
Conclusion: I. F ≥ P          II. G > P
