Aliasing is the process of giving a table or a table column a temporary name. Aliases are commonly used to either make the query easier to write, or more readable. An example of using table aliases to make a query shorter would be the following.
SELECT orders.description, orders.value, customers.email FROM orders INNER JOIN customers ON order.customer_id = customers.id;
By using table aliases, the query length can be greatly reduced.
SELECT o.description, o.value, c.email FROM orders AS o INNER JOIN customers AS c ON o.customer_id = c.id;
Note that aliases only last for the duration of a single query. If we were to run the previous query, and subsequently run the following query, it would fail.
SELECT o.description, o.value, c.email FROM o INNER JOIN c ON o.customer_id = c.id;
In addition to table aliases, we can give fields aliases as well. For example, we could reduce
customer_id to just
SELECT orders.customer_id AS c_id FROM orders INNER JOIN customers ON order.c_id = customers.id;
Alternatively, we could change
Customer ID, however, whenever we want an alias to contain spaces, we need to use either double quotes or square brackets.
SELECT orders.customer_id AS "Customer ID" FROM orders INNER JOIN customers ON order. "Customer ID" = customers.id;