Joins, Keys, Row Counts, and Duplicate Traps

About 80-100 minutes of guided work.

By the end of this module you can predict a join's row count before running it, recognise fan-out from the count alone, fix it without destroying data, and prove that a foreign key is actually kept.

Units

1. Unit 05.00: INNER, LEFT, and what each one drops
2. Unit 05.01: Predicting row count before you run the join
3. Unit 05.02: Diagnosing fan-out with a before-and-after count
4. Unit 05.03: Pre-aggregating the many-side as the fix
5. Unit 05.04: Finding orphans and broken key promises

Module work

• Activity
• Knowledge check
• Summary