DBMS and SQL
Learn how databases really store data, and write SQL you understand
6 lessons · 1.2 hours of reading
· Beginner · 3 free
Start from why a spreadsheet breaks down and build up to joins, grouping, normalisation and transactions. Every idea comes with a real table and a real query you can run.
Lessons
1
Why databases exist and what a table really is
The problems a spreadsheet cannot solve, and the precise meaning of a row and a column.
2
SELECT, WHERE, ORDER BY and LIMIT
The four clauses that answer ninety percent of real questions, with output shown for each query.
3
JOINs, with a worked two-table example
Why data is split across tables, and exactly which rows INNER and LEFT JOIN produce.
4
GROUP BY, aggregates, and HAVING vs WHERE
How grouping collapses rows, and the exact reason HAVING exists as a separate clause.
5
Keys and normalisation up to 3NF
One badly designed table, fixed step by step through 1NF, 2NF and 3NF.
6
Transactions, ACID, and what happens on a crash
What a transaction really guarantees, and how the database survives losing power mid-write.
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