# Joining

Another very common data operation is the join. Joins are a whole topic unto themselves, so in this course we'll just look at simple joins. If you'd like to learn more about joins, you can take a look here.

A join will combine two different tables along a column that they share. This column is called the key. Examples of keys here include the tailnum and carrier columns from the flights table.

For example, suppose that you want to know more information about the plane that flew a flight than just the tail number. This information isn't in the flights table because the same plane flies many different flights over the course of two years, so including this information in every row would result in a lot of duplication. To avoid this, you'd have a second table that has only one row for each plane and whose columns list all the information about the plane, including its tail number. You could call this table planes

When you join the flights table to this table of airplane information, you're adding all the columns from the planes table to the flights table. To fill these columns with information, you'll look at the tail number from the flights table and find the matching one in the planes table, and then use that row to fill out all the new columns.

Now you'll have a much bigger table than before, but now every row has all information about the plane that flew that flight!

Which of the following is not true?