Lesson 17 · Python
Databases: Joins, Aggregates & Subqueries
Stitch split tables back together: INNER and LEFT JOIN row by row, GROUP BY with COUNT, AVG and SUM, HAVING versus WHERE, and subqueries that answer questions inside questions.
Prerequisites: Databases: SQL Fundamentals
Learning objectives
By the end of this lesson, you will be able to:
- Explain why data is split across tables and how id columns connect them
- Join tables with INNER JOIN and LEFT JOIN, predicting which rows survive each
- Summarize groups with COUNT, AVG, SUM, MIN and MAX behind GROUP BY
- Filter rows with WHERE and groups with HAVING, choosing correctly between them
- Use subqueries in WHERE and FROM, and build a query from an English question step by step