MySQL Aliases (AS)

An alias is a temporary name you assign to a column or table within a query using the AS keyword. The alias only exists for the duration of that query — the actual column or table name in the database is never changed. Aliases make results easier to read, expressions more meaningful, and queries involving multiple tables much cleaner to write.

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Column Aliases

A column alias renames a column in the query's output. This is useful when column names are technical, abbreviated, or when you are displaying the result of an expression:

SELECT name AS student_name, city AS hometown, age AS years_old
FROM students;

student_name	hometown	years_old
Rahim Uddin	Dhaka	22
Sara Begum	Chittagong	20
Karim Ali	Sylhet	23

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Aliases for Expressions

Aliases are especially valuable when the SELECT list contains calculated expressions — without an alias, the output column would show the raw expression as its header:

-- Without alias: column header is "age + 1"
SELECT name, age + 1 FROM students;

-- With alias: column header is "next_year_age"
SELECT name, age + 1 AS next_year_age FROM students;

-- Combining columns into one readable field
SELECT
    CONCAT(first_name, ' ', last_name) AS full_name,
    YEAR(CURDATE()) - YEAR(birth_date)  AS age
FROM employees;

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Aliases with Spaces

If an alias contains spaces or special characters, wrap it in backticks or double quotes:

SELECT name AS `Full Name`, city AS `Home City`
FROM students;

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Using Aliases in ORDER BY

Column aliases can be referenced in the ORDER BY clause because MySQL evaluates ORDER BY after processing the SELECT list:

SELECT name, age + 1 AS next_year_age
FROM students
ORDER BY next_year_age DESC;

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Table Aliases

You can also alias a table name within a query. Table aliases are most useful when:

• Writing JOIN queries where you need to prefix columns with the table name.
• The table name is long and you want a short abbreviation throughout the query.

-- Without table alias: verbose
SELECT students.name, students.city
FROM students
WHERE students.age > 21;

-- With table alias: concise
SELECT s.name, s.city
FROM students AS s
WHERE s.age > 21;

In a JOIN, table aliases make the query far more readable:

SELECT s.name, c.course_name
FROM students AS s
JOIN enrollments AS e ON s.id = e.student_id
JOIN courses AS c ON e.course_id = c.id;

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Key Points to Remember

• An alias is a temporary name — it does not change the actual column or table name in the database.
• Use AS for column aliases to rename output columns and make expressions readable.
• Aliases with spaces must be wrapped in backticks or quotes — prefer underscores to avoid this.
• Column aliases can be used in ORDER BY but not in WHERE or HAVING.
• Table aliases shorten query syntax and are essential for clean JOIN queries.
• The AS keyword is optional, but always including it makes queries easier to understand.