SQL practice, session by session

Every live class gets 400 questions on real RetailMart data: 100 Easy, 100 Medium, 100 Hard and 100 Crazy hard, in small sets. Write the query, run it on the page, press Check. Your ticks stay in this browser.

Live class schedule Notes for every class SQL Playground

Module 1 · Foundations

Session 1

What is SQL?

100 questions · 0 solved

Session 2

How SQL is Organised

100 questions · 0 solved

Session 3

Writing Your First Queries

400 questions · 0 solved

Session 4

Data Types

400 questions · 0 solved

Session 5

Constraints

400 questions · 0 solved

Session 6

Keys: PRIMARY KEY, FOREIGN KEY & ON DELETE

400 questions · 0 solved

Session 7

DISTINCT & Filtering

400 questions · 0 solved

Session 8

Sorting & Pagination: ORDER BY, LIMIT & OFFSET

400 questions · 0 solved

Module 2 · Querying & Aggregation

Session 9

String Functions

Practice coming soon

Session 10

Date & Time Basics

Practice coming soon

Session 11

Conditional Logic & Casting: CASE WHEN & CAST

Practice coming soon

Session 12

NULL Handling: COALESCE, NULLIF & Three-Valued Logic

Practice coming soon

Session 13

Aggregate Functions: COUNT, SUM, AVG, MIN, MAX & STRING_AGG

Practice coming soon

Session 14

GROUP BY & HAVING

Practice coming soon

Session 15

Subtotals: ROLLUP & GROUPING()

Practice coming soon

Session 16

CUBE & GROUPING SETS

Practice coming soon

Session 17

Joins: The Idea & INNER JOIN + LEFT & RIGHT JOIN

Practice coming soon

Session 18

Anti-Joins: Finding What Never Happened

Practice coming soon

Session 19

FULL OUTER JOIN & Data Reconciliation

Practice coming soon

Session 20

CROSS JOIN: All Combinations

Practice coming soon

Session 21

Joining 3–5 Tables

Practice coming soon

Session 22

Self-Joins: Hierarchies & Pair Comparisons

Practice coming soon

Session 23

Set Operations: UNION, INTERSECT & EXCEPT

Practice coming soon

Module 3 · Subqueries, CTEs & Database Concepts

Session 24

Subqueries I: Scalar & Multi-Row (IN, ANY, ALL)

Practice coming soon

Session 25

Subqueries II: Derived Tables in FROM

Practice coming soon

Session 26

Correlated Subqueries & EXISTS

Practice coming soon

Session 27

LATERAL Joins

Practice coming soon

Session 28

Common Table Expressions (WITH)

Practice coming soon

Session 29

Recursive CTEs: Hierarchies & Trees

Practice coming soon

Session 30

Normalization: 1NF, 2NF, 3NF

Practice coming soon

Session 31

Transactions, ACID & Access Control

Practice coming soon

Module 4 · Window Functions & Performance

Session 32

Window Functions I: Ranking

Practice coming soon

Session 33

Window Functions II: Buckets & Distribution

Practice coming soon

Session 34

Window Functions III: Running Totals & Moving Averages

Practice coming soon

Session 35

Window Functions IV: Window Frames

Practice coming soon

Session 36

Window Functions V: LAG & LEAD

Practice coming soon

Session 37

Window Functions VI: FIRST_VALUE, LAST_VALUE & NTH_VALUE

Practice coming soon

Session 38

Query Plans I: Reading EXPLAIN

Practice coming soon

Session 39

Query Plans II: EXPLAIN ANALYZE

Practice coming soon

Session 40

Indexing I: B-Tree Indexes

Practice coming soon

Session 41

Indexing II: Composite, Partial & Covering Indexes

Practice coming soon

Module 5 · Analytics Power Tools & Programmable SQL

Session 42

Conditional Aggregation & FILTER

Practice coming soon

Session 43

Unpivoting Data

Practice coming soon

Session 44

Percentiles & Medians

Practice coming soon

Session 45

DISTINCT ON & Latest-Per-Group

Practice coming soon

Session 46

Time Series: generate_series & Gap-Filling

Practice coming soon

Session 47

Time Zones & Fiscal Calendars

Practice coming soon

Session 48

JSON I: JSON vs JSONB, -> and ->>

Practice coming soon

Session 49

JSON II: Containment & GIN Indexes

Practice coming soon

Session 50

Views

Practice coming soon

Session 51

Materialized Views

Practice coming soon

Session 52

Functions & Stored Procedures

Practice coming soon

Session 53

Triggers

Practice coming soon

Module 6 · Analyst Patterns

Session 54

Deduplication

Practice coming soon

Session 55

Cleaning Messy Data

Practice coming soon

Session 56

Cohort Analysis & RFM

Practice coming soon

Session 57

Funnels & Stickiness

Practice coming soon

Session 58

SQL from Python

Practice coming soon

Session 59

SQL for BI Tools & Dashboards

Practice coming soon

Want more questions?

The first question bank, by topic, as one download: a Markdown file per topic and a README on running them against RetailMart.

📦Older question bank, topic-wise28 topics · 11,200 questions · Easy to Crazy hard · questions only, no answers or checkerZIP · 280 KB ↓