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Tutorials, tips, and updates from the SQL Practice team.
SQL Window Functions: The Most Underrated Yet Powerful Feature Many Developers Miss
You know `GROUP BY`, `JOINs`, `CTEs`, and indexes. You can write decent queries and even optimize slow ones using execution plans. But there’s one SQL feature that sits in the sweet spot between...
Deloitte Data Engineer Interview Questions for 2-5 Years Experience: Complete Preparation Guide (2026)
Deloitte Data Engineer Interview Questions for 2-5 Years Experience: Complete Preparation Guide (2026) This guide focuses on the most frequently asked questions in Deloitte Data Engineer...
Deloitte SQL Interview Questions for 2-4 Years Experience: Complete Preparation Guide (2026)
Deloitte SQL Interview Questions for 2-4 Years Experience: Complete Preparation Guide (2026) This article compiles the most frequently asked SQL topics and questions at Deloitte for mid-level...
SQL GROUP BY Clause: Complete Guide with Examples and Optimization Tips
SQL GROUP BY Clause: Complete Guide with Examples and Optimization Tips The `GROUP BY` clause is one of the most powerful and frequently used features in SQL. It allows you to group rows that have...
Database Connection Pooling Explained — Why It Matters in 2026
Database Connection Pooling: Why It Matters and How to Implement It Opening and closing database connections is one of the most expensive operations in any application. Creating a new connection...
How to Read a SQL Execution Plan (+ Free Practice Tool)
How to Read a SQL Execution Plan (+ Free Practice Tool) An execution plan (also called a query plan or explain plan) is the database engine’s detailed roadmap for executing your SQL query. It...
SQL Query Optimization Techniques: A Comprehensive Overview
SQL Query Optimization Techniques: A Comprehensive Overview Query optimization is the process of improving SQL query performance by reducing execution time, CPU/memory usage, and I/O operations....
SQL Indexes for Performance Optimization: A Complete Guide
SQL Indexes for Performance Optimization: A Complete Guide Slow queries are one of the most common performance bottlenecks in relational databases. **Indexes** are one of the most powerful tools...
Understanding SQL Views, Materialized Views, and Common Table Expressions (CTEs)
Understanding SQL Views, Materialized Views, and Common Table Expressions (CTEs) In SQL, managing complex queries efficiently is crucial for performance, readability, and maintainability. Three...
Stored Procedures in PostgreSQL – When, Why & How to Use Them (From Noob to Pro)
Stored Procedures in PostgreSQL – When, Why & How to Use Them (From Noob to Pro) Hey, I’m Gaurav. When I first heard about Stored Procedures, I thought they were just “fancy functions” that old...
Top PostgreSQL Performance Bottlenecks in 2026 — Fix These First
Here's a clear, practical guide on PostgreSQL Performance Bottlenecks (what you meant by "postgres performance bottle necks"). Top PostgreSQL Performance Bottlenecks in 2026 These are the most...
Recursive CTEs in SQL – How to Think and Solve Hierarchical & Sequence Problems (From Noob to Pro)
Recursive CTEs in SQL – How to Think and Solve Hierarchical & Sequence Problems (From Noob to Pro) Hey, I’m Gaurav. When I first saw `WITH RECURSIVE`, I was terrified. The query had `UNION ALL`...
CTEs vs Temporary Tables in SQL – When to Use Which? (Complete Comparison + Thinking Guide)
CTEs vs Temporary Tables in SQL – When to Use Which? (Complete Comparison + Thinking Guide) Hey, I’m Gaurav. This was one of the most common questions I faced in SQL interviews: > “Should I use a...
CTEs in SQL (Common Table Expressions) – WITH Clause Explained Step by Step (From Noob to Pro)
CTEs in SQL (Common Table Expressions) – WITH Clause Explained Step by Step (From Noob to Pro) Hey, I’m Gaurav. When I first saw `WITH` clause in SQL, I thought it was just a fancy way to write a...
CUME_DIST() in SQL – Cumulative Distribution Explained (From Noob to Pro)
CUME_DIST() in SQL – Cumulative Distribution Explained (From Noob to Pro) Hey, I’m Gaurav. When I first saw `CUME_DIST()` in an SQL interview, I had no clue what it meant. The interviewer...
SQL Window Frame Clauses: ROWS vs RANGE (With Practice Examples)
Understanding Window Frame Clauses in SQL – ROWS vs RANGE (With Simple Examples) Hey, I’m Gaurav. When I first learned window functions, I was comfortable with `PARTITION BY` and `ORDER BY`. But...
Complete Guide to Window Functions in SQL – NTILE, SUM, AVG, COUNT, MIN, MAX with OVER() (From Noob to Pro)
Complete Guide to Window Functions in SQL – NTILE, SUM, AVG, COUNT, MIN, MAX with OVER() (From Noob to Pro) Hey, I’m Gaurav. After learning `RANK()`, `DENSE_RANK()`, `ROW_NUMBER()`, `LAG()`, and...
LAG() and LEAD() in SQL – How to Think and Solve Questions Step by Step (From Noob to Pro)
LAG() and LEAD() in SQL – How to Think and Solve Questions Step by Step (From Noob to Pro) Hey, I’m Gaurav. When I first saw `LAG()` and `LEAD()` in an interview, I had no idea what they were. The...
RANK(), DENSE_RANK(), and ROW_NUMBER() in SQL – How to Think and Solve Questions Step by Step
RANK(), DENSE_RANK(), and ROW_NUMBER() in SQL – How to Think and Solve Questions Step by Step Hey, I’m Gaurav. When I first saw ranking questions in SQL interviews, I was completely confused. The...
Types of Views in SQL – Simple, Complex & Materialized Views Explained (With Examples & Practice)
Types of Views in SQL – Simple, Complex & Materialized Views Explained (With Examples & Practice) Hey, I'm Gaurav. When I first heard about Views in SQL interviews, I thought they were just “some...
Mastering Window Functions in SQL – How to Think & Solve Questions Step by Step (From Noob to Pro)
Mastering Window Functions in SQL – How to Think & Solve Questions Step by Step (From Noob to Pro) Hey, I'm Gaurav. When I first saw window functions in SQL interviews, I was completely lost. The...
Relationships in SQL – One-to-One, One-to-Many, Many-to-Many Explained
Relationships in SQL – One-to-One, One-to-Many, Many-to-Many Explained How to Think About It (From Noob Brute Force to Proper Approach) Hey, I’m Gaurav. When I first saw questions like “Show all...
SQL Functions – Aggregate, Scalar & Window Functions Explained (With Examples & Practice)
Functions are one of the most powerful parts of SQL. Once I understood them properly, my queries went from basic to professional-level overnight. Today, we're covering the three main types of SQL...
Database Normalization in SQL – 1NF to BCNF Full Guide (With Examples & Practice Questions)
Normalization was one of those topics that felt super theoretical when I first read about it. I thought, "Why bother? My queries work fine." Then I saw a real messy table in an interview question...
Types of Indexes in SQL – Complete Guide for Interviews
Indexes were one of those topics that confused me a lot during interview prep. I knew they make queries faster, but when someone asked "What type of index would you use for full-text search?" or...
Keys in SQL – Primary Key, Foreign Key, Unique Key & Composite Key Explained (With Examples & Practice)
In my early days of SQL interview prep, I used to mix up Primary Key, Foreign Key, and Unique Key all the time. Interviewers love asking about keys because they test your understanding of data...
Understanding Relationships in SQL - (With Examples & Practice)
When I first started learning SQL for interviews, I could write basic SELECT queries just fine. But the moment they asked something like "show all orders with customer names and product details,"...
Database Connection Pooling Explained — Why It Matters in 2026
In a production-grade application, every incoming request typically requires access to the database. The backend establishes a database connection, executes the query, returns the response, and...
Mastering INNER JOIN in SQL: Complete Guide with Examples & Practice Questions (2026 Interviews)
When I first started preparing for SQL interviews, INNER JOIN was the concept that tripped me up the most. I could handle single-table queries fine, but as soon as they asked something like "show...
How to understand bottlenecks in sql queries
Finding a bottleneck in a SQL query is a lot like being a detective at a busy intersection. You know traffic is backed up, but you need to figure out if it’s because the light is too short, the...