Good job! We can do one more thing with our columns: rename them. Up till now, the column named
id was always shown as
id in the result. Now we can change it:
person.id AS person_id,
car.id AS car_id
ON person.id = car.owner_id;
After the column name, e.g.
person.id, we use the new keyword
AS and we put the new name after it (
person_id). We can repeat this process with every column.
The new name is just an alias, which means it's temporary and doesn't change the actual column name in the database. It only influences the way the column is shown in the result of the specific query. This technique is often used when there are a few columns under the same name coming from different tables. Normally, when SQL displays columns in the result, there is no information about the table that a specific column is part of.
In our example, we had two columns
id, so we renamed them to
car_id respectively. Now, if we see the columns in the result, we will know which column comes from which table.