SQL Interview Questions

50 Pages • 50 Interview Questions

A practical interview guide where ONE PAGE = ONE INTERVIEW QUESTION.

Every page gives you:

• 🎯 What the interviewer wants to hear
• ⚙️ How it works — simple step-by-step explanation
• 🔄 Flow Diagram — quick visual recall
• 💻 Exact Query — ready to write on the board
• 📌 Expected Output — what to explain after the query
• ☕ Java Note — JDBC / JPA / Hibernate / Spring Boot connection

📚 Topics Covered

1. Core SQL

• SELECT, WHERE, HAVING
• LIKE, IN, NULL
• ORDER BY, LIMIT
• GROUP BY & Aggregations

2. Top Interview Queries

• Maximum Salary
• 2nd Highest Salary
• Nth Highest Salary
• Above Average Salary
• Department Average Salary
• Top Salary by Department

3. JOINs

• INNER vs LEFT JOIN
• SELF JOIN — Employee & Manager
• Anti-Join
• FULL OUTER JOIN — MySQL approach

4. Subqueries & Logic

• Correlated vs Uncorrelated
• EXISTS vs IN vs NOT EXISTS
• UNION vs UNION ALL
• CASE WHEN
• Scalar Subquery
• Relational Division — A + B

5. Advanced SQL

• CTE
• Recursive CTE — Org Hierarchy
• ROW_NUMBER vs RANK vs DENSE_RANK
• LAG / LEAD
• Running Total
• Duplicate Handling

6. SQL Performance

• Clustered vs Non-Clustered Index
• Composite & Covering Index
• EXPLAIN / EXPLAIN ANALYZE
• OFFSET vs Keyset Pagination
• COUNT(*) on Large Tables

7. Java + SQL

• ACID & Transactions
• Isolation Levels
• Dirty / Non-Repeatable / Phantom Reads
• JDBC Transactions
• SQL Injection
• Statement vs PreparedStatement
• Batch Processing
• Views vs Materialized Views
• Stored Procedure vs Function
• Constraints

8. Hibernate Killer Questions

• N+1 Problem
• JOIN FETCH
• EntityGraph
• @BatchSize
• Lazy vs Eager Loading
• Deadlock & Retry Handling

🚀 The Interview Flow

Understand → Explain → Draw → Write Query → Explain Output → Connect to Java

50 Questions. 50 Pages. Interview Ready.