What are SQL aliases and how to use them

Short answer

Aliases are temporary names assigned to tables or columns using the AS keyword. They make queries shorter and results clearer.

Steps

1. Column alias: SELECT first_name AS fname FROM employees;
2. Table alias: SELECT e.first_name FROM employees AS e;
3. Expression alias: SELECT price * quantity AS total FROM order_items;
4. Use aliases in ORDER BY: SELECT first_name AS name FROM employees ORDER BY name;
5. Reference aliased tables in joins: SELECT o.id, c.name FROM orders AS o JOIN customers AS c ON o.customer_id = c.id;

Tips

• Aliases are especially useful in self-joins where the same table appears twice.
• Some databases allow omitting AS, but including it improves readability.

Common issues

• Aliases defined in SELECT cannot be used in the same WHERE clause because of logical processing order.
• Spaces in aliases require quoting: AS "First Name".r