FAQ: Multiple Tables - Primary Key vs Foreign Key


This community-built FAQ covers the “Primary Key vs Foreign Key” exercise from the lesson “Multiple Tables”.

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This exercise can be found in the following Codecademy content:

Web Development
Data Science

Learn SQL

FAQs on the exercise Primary Key vs Foreign Key

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Why I have to use JOIN and not LEFT JOIN?


Do you understand the difference between (inner) join and left join? Knowing the differences can help

left join selects all rows from the left and table and the matching records from the right table
inner join select all rows which match from both tables

Translating to the exercise at hand: left join would give all classes, even the classes with no students, while inner join while only give the classes with students (at least one student has to be in the class for the row to be returned by the query)