Page 163 - SQL

SELECT
Customers.PhoneNumber,
Customers.Email,
Customers.PreferredContact,
Orders.Id AS OrderId
FROM
Customers
LEFT JOIN
Orders ON Orders.CustomerId = Customers.Id

*AS OrderId means that the Id field of Orders table will be returned as a column named OrderId. See
selecting with column alias for further information.

To avoid using long table names, you can use table aliases. This mitigates the pain of writing long
table names for each field that you select in the joins. If you are performing a self join (a join
between two instances of the same table), then you must use table aliases to distinguish your
tables. We can write a table alias like Customers c or Customers AS c. Here c works as an alias for
Customers and we can select let's say Email like this: c.Email.

SELECT
c.PhoneNumber,
c.Email,
c.PreferredContact,
o.Id AS OrderId
FROM
Customers c
LEFT JOIN
Orders o ON o.CustomerId = c.Id

SELECT Using Column Aliases

Column aliases are used mainly to shorten code and make column names more readable.

Code becomes shorter as long table names and unnecessary identification of columns (e.g., there
may be 2 IDs in the table, but only one is used in the statement) can be avoided. Along with table
aliases this allows you to use longer descriptive names in your database structure while keeping
queries upon that structure concise.

Furthermore they are sometimes required, for instance in views, in order to name computed
outputs.

All versions of SQL

Aliases can be created in all versions of SQL using double quotes (").

SELECT
FName AS "First Name",
MName AS "Middle Name",
LName AS "Last Name"
FROM Employees

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