February 2024
Beginner
352 pages
8h 16m
English
book
Learn Python the Hard Way: A Deceptively Simple Introduction to the Terrifyingly Beautiful World of Computers and Data Science, 5th Edition
by Zed A. Shaw
Content preview from Learn Python the Hard Way: A Deceptively Simple Introduction to the Terrifyingly Beautiful World of Computers and Data Science, 5th Edition
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Exercise 59
SQL Relationships
Our final exercise is going to cover the concept of relations in SQL. In technical terms every table is a relation, but we’re going to be more specific and talk about tables that are connected to other tables in various ways.
One-to-Many (1:M)
A “relation” in SQL is a method of using id columns in tables to associate one table to another through a “one-to-many” or “many-to-many” relationship. In our ECB data we have a rate for each country and a currency that rate applies to. We can say the following about this relationship between rate and currency:
“A Rate has one Currency, and a Currency has many Rate.”
In our 2NF version of the ECB data, the first part is modeled by placing a currency_id in the rate table so ...
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