Aliases (AS)

SQL Aliases (AS)

Aliases are temporary names given to columns or tables to make queries more readable.

💡 Aliases don't change actual column or table names — they just rename them for the current query.

Column Aliases

SELECT column_name AS alias_name FROM table_name;

Examples

SELECT
    first_name AS "First Name",
    last_name AS "Last Name",
    salary * 0.1 AS "Bonus Amount"
FROM employees;

The AS Keyword is Optional

SELECT first_name "First Name", last_name "Last Name"
FROM employees;

Table Aliases

SELECT c.first_name, c.last_name, o.total
FROM customers AS c
INNER JOIN orders AS o ON c.id = o.customer_id;

-- AS is optional for tables too:
SELECT c.first_name, o.total
FROM customers c
INNER JOIN orders o ON c.id = o.customer_id;

Aliases with Expressions

SELECT
    name,
    price,
    stock,
    price * stock AS inventory_value,
    CASE
        WHEN stock = 0 THEN 'Out of Stock'
        WHEN stock < 10 THEN 'Low Stock'
        ELSE 'In Stock'
    END AS stock_status
FROM products;

⚠️ You CANNOT use column aliases in the WHERE clause because WHERE is evaluated before SELECT.

✏️ Exercise: Write a query that uses table aliases to join 'customers' (alias c) with 'orders' (alias o)

See Solution

SELECT c.first_name, c.last_name, o.total, o.order_date
FROM customers c
INNER JOIN orders o ON c.id = o.customer_id;

✅ Key Takeaways

1. Column aliases rename columns in the result set
2. Table aliases make queries shorter and cleaner
3. Use AS for clarity (though it's optional)
4. Aliases work in ORDER BY but not in WHERE
5. Aliases are essential with joins and expressions