Module 02 · Handling data

Storage and query

A list of dicts cannot enforce anything. A table can, and the moment you have one you can ask questions, which is when you find out what the join has been quietly dropping.

4 lessons · 3 graded exercises·3 hours·intermediate·Prerequisite: Cleaning and validation

Why a table

20 min

A list of dicts holds whatever you put in it. A table refuses, and the refusal is the feature you are actually buying.

Loading a table

30 min · exercise

Creating the table, inserting in one transaction, and deciding what a duplicate key means. Every one of those is a decision the load makes on your behalf if you do not make it.

Indexes and the plan

30 min · exercise

The query planner will tell you exactly what it is about to do, in one line, and almost nobody asks. Learning to read that line is the cheapest performance skill there is.

The rows a join loses

30 min · exercise

An inner join silently drops rows that do not match. That is what it is for and it is also where most quiet data bugs come from, so count what it dropped every time.