SQL Aliases

Introduction

Aliases rename columns or tables in a query for readability. Column aliases use AS (or just space). Table aliases shorten join queries.

Understanding the topic

Core concepts to understand:

• SELECT name AS full_name FROM users;
• FROM orders o JOIN users u ON u.id = o.user_id;
• Aliases exist only for the duration of the query.
• Use them for: computed columns, joins, subqueries.
• Quoted aliases preserve case: AS "Full Name".

Syntax reference

Visual workflow / architecture:

SELECT u.name        AS user_name,
       count(o.id)   AS total_orders,
       sum(o.amount) AS revenue
FROM   users  u
LEFT JOIN orders o ON o.user_id = u.id
GROUP  BY u.id, u.name;

SELECT <col>  AS <col_alias>,
       <expr> AS <expr_alias>
FROM   <table> AS <table_alias>;

SELECT u.name           AS customer,
       COUNT(o.id)      AS total_orders
FROM   users  AS u
LEFT JOIN orders AS o ON o.user_id = u.id
GROUP  BY u.id, u.name;

Real-world use

Reports, BI dashboards and ETL pipelines rely on aliases to give clean column names that match downstream UI/CSV expectations.

Best practices

• Always alias join tables with short, meaningful letters.
• Always alias computed columns (count(*) AS total).
• Use full descriptive aliases in BI/report queries.

Hands-on exercise

Interview preparation — practice these questions:

• Q1. Why use table aliases?
• Q2. Are aliases case sensitive?
• Q3. Can you reference a column alias in WHERE?
• Q4. AS keyword — required or optional?
• Q5. Quoting aliases — when needed?