When and how to use table aliases

The syntax for an inner join that uses table aliases

      SELECT select_list
      FROM table_1 [AS] n1 
      [INNER] JOIN table_2 [AS] n2 ON n1.column_name operator n2.column_name 
      [[INNER] JOIN table_3 [AS] n3 ON n2.column_name operator n3.column_name]...

An inner join with aliases for all tables

      SELECT firstName, lastName, orderDate
      FROM customers c 
      INNER JOIN orders o ON c.customerID = o.customerID 
      ORDER BY orderDate;

An inner join with aliases for four tables

      SELECT firstName, lastName, o.orderID, productName, itemPrice, quantity
      FROM customers c 
      INNER JOIN orders o ON c.customerID = o.customerID 
      INNER JOIN orderItems oi ON o.orderID = oi.orderID 
      INNER JOIN products p ON oi.productID = p.productID 
      ORDER BY o.orderID;

    Description
      A table alias is an alternative table name assigned in the FROM clause.
The AS keyword is optional.
If you assign an alias to a table, you must use that alias to refer to the table throughout your query. You can’t use the original table name.
Use table aliases whenever they simplify or clarify the query. Avoid using them when they make a query more confusing or difficult to read.

    

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