Interview Prep

SQL100: Relational Data Ops

Master everything from basic SELECT queries to advanced window functions, query optimization, and PostgreSQL-specific features.

Level

Relational Ops

Questions

100+

Focus

PostgreSQL Standard

Format

Industry-Ready

SQL Basics

8 questions

JOINs (Deep Dive)

4 questions

Keys, Constraints & Data Integrity

4 questions

Indexes & Performance

4 questions

Subqueries, CTEs & Views

3 questions

Window Functions (Deep Dive)

4 questions

Transactions & ACID Properties

3 questions

Normalization & Database Design

2 questions

Advanced SQL Concepts

8 questions

PostgreSQL — Specific Features

17 questions

Query Optimization & Performance

5 questions

Common Interview Patterns & Problems

38 questions

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SQL100: Relational Data Ops

SQL Basics

What is SQL and what is it used for?

What is a relational database?

What is the difference between DDL, DML, DCL, and TCL?

What is the SELECT statement and how does it work?

What is the WHERE clause and what operators can you use?

What are aggregate functions and what is GROUP BY?

What is the difference between WHERE and HAVING?

In what order does SQL execute clauses?

JOINs (Deep Dive)

What is a JOIN and what are the different types?

What is a SELF JOIN and when do you use it?

What is a CROSS JOIN?

JOIN vs subquery — what's the difference and when to use which?

Keys, Constraints & Data Integrity

What is a Primary Key?

What is a Foreign Key and how does it enforce data integrity?

What are the different SQL constraints?

What is the difference between UNIQUE and PRIMARY KEY?

Indexes & Performance

What an index and how does it speed up queries?

What is a composite index and the left prefix rule?

What is EXPLAIN / EXPLAIN ANALYZE and how do you use it?

When should you NOT add an index?

Subqueries, CTEs & Views

What is a subquery and what are the different types?

What is a CTE and why use it over a subquery?

What is a View and when should you use it?

Window Functions (Deep Dive)

What are window functions and how are they different from GROUP BY?

What are ROW_NUMBER, RANK, and DENSE_RANK?

What are LAG and LEAD window functions?

What are FIRST_VALUE, LAST_VALUE, and NTILE?

Transactions & ACID Properties

What are ACID properties?

What are transaction isolation levels?

What is a SAVEPOINT?

Normalization & Database Design

What is normalization? Explain 1NF, 2NF, and 3NF.

What is denormalization and when is it used?

Advanced SQL Concepts

What is the difference between UNION, UNION ALL, INTERSECT, and EXCEPT?

What is the difference between EXISTS and IN?

What is a PIVOT / CROSSTAB query?

What are stored procedures and functions?

What are triggers in SQL?

What are COALESCE, NULLIF, and ISNULL?

What is the CASE expression?

What is the difference between TRUNCATE, DELETE, and DROP?

PostgreSQL — Specific Features

What makes PostgreSQL different from other databases?

What data types does PostgreSQL support?

How do you work with JSONB in PostgreSQL?

How do arrays work in PostgreSQL?

What is full-text search in PostgreSQL?

What are sequences in PostgreSQL?

What is MVCC (Multi-Version Concurrency Control) in PostgreSQL?

What is table partitioning in PostgreSQL?

What are PostgreSQL roles and permissions?

What are PostgreSQL extensions?

What is LISTEN/NOTIFY in PostgreSQL?

What is UPSERT (INSERT ON CONFLICT) in PostgreSQL?

What is pg_dump and how do you backup PostgreSQL?

What are PostgreSQL schemas?

What is logical replication in PostgreSQL?

What is the RETURNING clause in PostgreSQL?

What are table statistics and how do they affect query planning?

Query Optimization & Performance

What are the most common causes of slow SQL queries?

What are covering indexes and index-only scans?

How do you paginate results efficiently?

What is VACUUM and ANALYZE in PostgreSQL and why are they important?

How do you monitor slow queries in PostgreSQL?

Common Interview Patterns & Problems

How do you find duplicate rows in a table?

How do you find the second (or Nth) highest salary?

How do you find employees who earn more than their manager?

How do you get the top N products per category?

How do you calculate a running total / cumulative sum?