Master Technical Database Interviews: Introducing SQL Interview Trainer (512 Q&A)

Hello developers, data enthusiasts, and software engineers! 👋

Preparing for SQL and database technical interviews can be deceptively tricky. Almost every tech role — whether you are a Backend Engineer, Data Analyst, Data Engineer, or DBA — requires writing efficient SQL. Yet candidates often stumble when questions move past simple SELECT * FROM table:

• How do query planners actually evaluate your joins?
• When will a function on a column break index utilization (SARGability)?
• How do transaction isolation levels prevent Dirty Reads or Phantom Reads?
• How can complex data aggregations be solved using modern Window Functions?

To help you conquer these hurdles, I'm thrilled to introduce SQL Interview Trainer — an interactive Android application designed to help Junior and Middle developers master practical SQL, understand DB internals, and walk into interviews with total confidence!

💡 What is SQL Interview Trainer?

Rather than testing trivial syntax trivia, SQL Interview Trainer focuses on the core concepts and operational mechanics of relational databases. Featuring 512 curated questions & answers (split evenly into 256 Junior and 256 Middle levels), it systematically prepares you for technical screens across PostgreSQL, MySQL, SQL Server, and Oracle concepts.

📚 8 Core Knowledge Modules

Every question is categorized across 8 core topics mirroring real-world interview loops:

1. 🔍 SQL Basics & Data Retrieval — Query structure, filtering (WHERE vs. HAVING), aggregation, sorting, and NULL handling.
2. 🔗 Joins, Relationships & Set Operations — Inner/Outer/Cross Joins, join algorithms, cartesian products, and set operations (UNION, INTERSECT, EXCEPT).
3. 📑 Subqueries, CTEs & Views — Correlated subqueries, Common Table Expressions (Recursive CTEs), Materialized Views, and performance tradeoffs.
4. 🪟 Window Functions & Analytical SQL — ROW_NUMBER(), RANK(), DENSE_RANK(), LEAD(), LAG(), window frames, and running calculations.
5. 🏛️ Database Design, Schemas & Normalization — Entity relationships, primary/foreign keys, 1NF through BCNF normalization, and denormalization strategies.
6. 🛡️ Transactions, ACID & Concurrency Control — Atomicity, Consistency, Isolation, Durability, isolation levels (Read Committed, Repeatable Read, Serializable), locking, and MVCC.
7. ⚡ Indexing, Performance Tuning & Query Plans — B-Tree vs. Hash indexes, covering indexes, query plans (EXPLAIN / ANALYZE), index scan vs. sequential scan, and SARGable predicates.
8. 💼 Practical Coding & Complex Business Queries — Solving real-world reporting queries, handling gaps and islands, deduplication, and tricky corner cases.

🌟 Key App Modes & Features

• 📖 Interactive Study Mode: Browse questions by category at your own pace with clean, syntax-highlighted SQL snippets and detailed theoretical rationale.
• 🎯 Custom Mock Interviews: Build custom test sessions by selecting your target tier (Junior or Middle) and adjusting the questions count per module.
• ⏱️ Exam Simulation Mode: Put your knowledge to the test against a countdown timer under realistic interview pressure.
• 📊 Categorical Performance Analytics: Pinpoint weak areas and review historical scores to focus your study time where it matters most.
• 🔥 Streaks & Achievements: Maintain study momentum and build consistent interview-prep habits with daily streaks.
• 🌍 Full Localization: Fully translated into 5 languages: English, Ukrainian (Українська), German (Deutsch), Spanish (Español), and French (Français).

📲 How to Get Started (Android)

1. Download the signed .apk file directly from this itch.io page.
2. Open the file on your Android device.
3. Allow "Install apps from unknown sources" in your settings if prompted.
4. Launch the app and start leveling up your SQL mastery today!

💬 Feedback & Community

This app was built for the developer and data community. If you spot an issue, have ideas for new complex scenarios, or successfully land a new job after practicing with the app — please leave a comment below!

Good luck with your interviews, and write clean queries! 🚀