SQL

Install PostgreSQL 18 on Windows or Mac, connect with DBeaver, try psql in a terminal, and load the Chai Corner database so every later lesson runs on your own machine.

Write your first queries: read a table with SELECT and FROM, pick columns, do maths and rename with AS, keep rows with WHERE, AND, OR, NOT, IN, BETWEEN, LIKE and ILIKE, and handle NULL.

Sort results with ORDER BY, take a page of rows with LIMIT and OFFSET, and remove repeated rows with DISTINCT.

Choose the right data type: integers, numeric and float, char, varchar and text, dates and times, boolean, UUID and JSON, and convert between them with CAST and ::.

Use text, number and date functions, make decisions inside a query with CASE WHEN, and handle missing values with COALESCE and NULLIF.

Summarise data with COUNT, SUM, AVG, MIN and MAX, group rows with GROUP BY, filter groups with HAVING, learn the order SQL runs your query, use FILTER, and build the Café Sales Report.

Design a database: why data is split into tables, primary and foreign keys, one to one, one to many and many to many relationships, normalisation to 3NF, and drawing an ER diagram.

Combine tables with INNER, LEFT, RIGHT, FULL OUTER, self and CROSS joins, join three or more tables, and avoid the common JOIN mistakes that give duplicates and wrong totals.

Put a query inside a query: subqueries in WHERE, SELECT and FROM, IN, EXISTS and the NOT IN with NULL trap, correlated subqueries, UNION, INTERSECT and EXCEPT, then build Customer Insights.

Create your own tables with columns, types and constraints, link them with foreign keys and ON DELETE, change them with ALTER TABLE, and know when to use DROP, TRUNCATE or DELETE.

Change data safely: INSERT, UPDATE and DELETE without accidents, soft delete, UPSERT with ON CONFLICT, and importing and exporting CSV files.

Keep data correct with transactions: BEGIN, COMMIT, ROLLBACK and SAVEPOINT, ACID in plain words, isolation levels, locks and deadlocks, then build Chai Corner Online Orders.

Break long queries into small, readable named steps with WITH, chain many CTEs, and walk trees and chains with recursive CTEs.

Rank, number and compare rows with window functions: ROW_NUMBER, RANK, DENSE_RANK, PARTITION BY, running totals, moving averages, LAG, LEAD, NTILE, and top N per group.

Save queries as views and materialized views, write your own functions, procedures and triggers, store flexible data with JSONB, then build the Business Dashboard.

See how an index finds a row without a full scan, create indexes on 100,000 orders, get multi-column order right, read EXPLAIN and EXPLAIN ANALYZE, and learn when indexes hurt.

Fix the usual slow query patterns, page fast with keyset pagination, see how the planner uses statistics, ANALYZE and VACUUM, and tune a query from 3 seconds to 1 millisecond.

Protect a database: users and roles with GRANT and REVOKE, how parameterised queries stop SQL injection, backups with pg_dump and pg_restore, and row-level security.

Use SQL from Python with psycopg and safe queries, see what an ORM is and when raw SQL is better, and change a live database safely with migrations.

Analyse data with SQL: clean messy data, build date reports with week and month buckets, pivot rows into columns, and export results to Google Sheets for a chart.

See what changes in MySQL, SQLite and BigQuery, solve classic interview problems, design a database in an interview, answer the top 50 SQL interview questions, follow a 30-day practice plan, and finish with an interview mock and the capstone.