RRB JE Computer Science & IT — Solved Practice Question Bank

Q: What is the main difference between a primary key and a foreign key? Sol: A primary key uniquely identifies each record within its OWN table and cannot be NULL; a foreign key is a column that references a primary key in ANOTHER table, enforcing a relationship between tables. Q: Which SQL JOIN returns all rows from the left table, with NULLs for unmatched right-table columns? Sol: LEFT JOIN. Q: What does the "I" in ACID properties stand for, and what does it ensure? Sol: Isolation — it ensures that concurrently executing transactions do not interfere with each other's intermediate states, as if they ran sequentially.

Q: Which layer of the OSI model is responsible for routing packets between different networks? Sol: Network layer (Layer 3). Q: Why is UDP preferred over TCP for live video streaming? Sol: UDP has lower overhead and no retransmission delay — for real-time streaming, a dropped packet causing a brief glitch is preferable to the delay TCP's retransmission/acknowledgment would introduce. Q: Name the four Coffman conditions necessary for a deadlock to occur. Sol: Mutual Exclusion, Hold and Wait, No Preemption, and Circular Wait — all four must hold simultaneously.

Q: What is the average-case time complexity of Quick Sort? Sol: O(n log n) — though its worst case (already sorted/reverse-sorted input with poor pivot choice) is O(n²). Q: Which data structure follows LIFO order, and where is it commonly used? Sol: Stack — commonly used in function call management (call stack) and recursion, and to implement "undo" operations. Q: What must every correctly written recursive function have to avoid infinite recursion? Sol: A base case (termination condition) that the recursive calls move progressively closer to.