SQL practice problems | Coding With Joseph

SQL

Three levels of hands-on database practice. Every question runs on a real database that resets for each run.

Level 1

Foundations

Read rows out of a table, put rows in, and build a table of your own.

Pick columns, filter rows with WHERE, then sort and limit

Add rows, change values and remove rows — carefully

Design a table: columns, types, keys and defaults

Level 2

Bring tables together, summarise them, and reshape what is already there.

INNER and LEFT joins across two, three or more tables

COUNT, SUM, AVG, MIN, MAX, GROUP BY and HAVING

Queries inside queries: IN, EXISTS, scalar and derived tables

Add, rename and drop columns; drop tables, views and indexes

Level 3

The tools a second database course expects: CTEs, windows, views, constraints.

WITH clauses that name a step, chain steps, and recurse

RANK, ROW_NUMBER, running totals and LAG over partitions

Saved queries with CREATE VIEW, speed-ups with CREATE INDEX

NOT NULL, UNIQUE, CHECK, DEFAULT and foreign keys that protect data