Example
SELECT
PhoneNumber,
Email,
PreferredContact
FROM Customers
This statement will return the columns PhoneNumber, Email, and PreferredContact from all rows of the Customers table. Also the columns will be returned in the sequence in which they appear in the SELECT clause.
The result will be:
| PhoneNumber | PreferredContact | |
|---|---|---|
| 3347927472 | [email protected] | PHONE |
| 2137921892 | [email protected] | |
| NULL | [email protected] |
If multiple tables are joined together, you can select columns from specific tables by specifying the table name before the column name: [table_name].[column_name]
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
