That's right! Aliases are also convenient in other cases. Let's analyze the following situation:
We want to put information about children and their mothers into a database. At some point, we would also like to show children together with their mothers using a join.
Let's say we store both children and mothers in the same table
Person, which has a column named
MotherID. This column contains the ID of a mother; this ID is taken from the very same table person.
The question is: can we join the table
Person with itself? The answer is simple: yes, we can! You can't write
Person JOIN Person
in your SQL query, but you can provide two different aliases for the same table:
FROM Person AS P1
INNER JOIN Person AS P2
ON P1.ID = P2.MotherID;
Thanks to the aliases, the database engine will use the same table twice—the first time to look for children, and the second time to look for their mothers.