Aliases in MySQL are used to give a temporary, alternative name to a table or a column in a query. They help improve readability and make query results more user-friendly.

1. Column Alias

A column alias renames a column in the output of a query.

Syntax

SELECT column_name AS alias_name FROM table_name;

• AS is optional.
• The alias is only used in the result set, not in the actual database.

Example

SELECT first_name AS Name, last_name AS Surname FROM employees;

Result:

+-------+--------+| Name  | Surname |+-------+--------+| John  | Doe    || Jane  | Smith  |+-------+--------+

Using Alias Without AS

SELECT first_name Name, last_name Surname FROM employees;

This works the same way.

Using Aliases with Spaces

If the alias contains spaces, use backticks (`) or double quotes (""):

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

2. Table Alias

A table alias assigns a temporary name to a table, useful when working with joins or subqueries.

Syntax

SELECT t.column_name FROM table_name AS t;

Example

SELECT e.first_name, e.last_name, d.department_nameFROM employees AS eJOIN departments AS d ON e.department_id = d.id;

Result:

+-----------+----------+----------------+| first_name | last_name | department_name |+-----------+----------+----------------+| John      | Doe      | HR             || Jane      | Smith    | IT             |+-----------+----------+----------------+

• e is an alias for the employees table.
• d is an alias for the departments table.

Using Table Aliases Without AS

SELECT e.first_name, e.last_name FROM employees e;

Works the same way.

3. Aliases in Calculated Columns

Aliases are helpful when working with expressions or calculations.

Example

SELECT price, price * 0.9 AS discounted_price FROM products;

Key Points

✅ Aliases are temporary and only last during query execution.
✅ Use them to make queries cleaner and more readable.
✅ Column aliases help rename column headers.
✅ Table aliases simplify complex queries, especially with joins.

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