Surprised, huh? If there are 8 movies and 5 directors, most people will say that we'll get 5, 8 or 13 rows in the result. This is not true.
We've got 40 rows altogether because SQL takes every single movie and joins it with every possible director. So we now have 8 * 5 = 40 rows!
Why did it happen? SQL doesn't know what to do with the results from the two tables, so it gave you every possible connection. How can we change it? Take a look:
FROM person, car
WHERE person.id = car.owner_id;
We've set a new condition in the
WHERE clause. We now see only those connections where
person is the same as
car. Makes sense, right?
Take a closer look at how we provide the information about columns in the
WHERE condition. If you have multiple tables, you should refer to specific columns by giving the name of the table and the column, separated by a dot (
.). As a result, the column
owner_id from the table
car.owner_id and so on.