SQL Tutorial

1. SQL Introduction

What SQL is, the relational model, and the users/orders/products schema used throughout this section.

2. SELECT and Filtering

SELECT, WHERE, comparison and logical operators, LIKE, IN, BETWEEN, ORDER BY, and LIMIT.

3. SQL Joins

INNER, LEFT, RIGHT, and FULL joins explained with examples, plus self-joins.

4. Aggregation and Grouping

COUNT, SUM, AVG, MIN, MAX, GROUP BY, and the difference between WHERE and HAVING.

5. Subqueries and CTEs

Subqueries in WHERE and FROM, correlated subqueries, common table expressions, and recursive CTEs.

6. Window Functions in Depth

ROW_NUMBER, RANK, DENSE_RANK, LAG/LEAD with PARTITION BY, running totals, and top-N-per-group.

7. Query Performance and Tricky Queries

Reading a query plan conceptually, plus classic puzzles: gaps in a sequence, second-highest value, and hierarchical self-joins.

8. SQL Interview Questions

Real SQL interview questions and answers covering joins, subqueries, NULL handling, and more.