🗄️ SQL

Ask questions of a database: filter, group and join data. A staple of placement tests.

1. Getting started with SQL
Tables, rows, and the practice data used in these lessons.
2. Filtering and sorting
WHERE, AND, IN, LIKE, ORDER BY and LIMIT.
3. Counting and grouping
COUNT, SUM, AVG, GROUP BY and HAVING.
4. Joins
Combine tables with INNER JOIN and LEFT JOIN.
5. Subqueries
Use the result of one query inside another.
6. Changing data
INSERT, UPDATE and DELETE safely.
7. Tables, keys and normalisation
Keys, constraints, indexes and the normal forms.
8. SQL quick reference
Clause order and common functions on one page.

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