🪞 SQL Aliases – Rename Columns and Tables for Clarity

🧲 Introduction – What are SQL Aliases?

SQL Aliases are temporary names assigned to columns or tables. They make queries easier to read, simplify results, and support advanced operations like joins, subqueries, and aggregation.

🎯 In this guide, you’ll learn:

• How to create aliases for columns and tables
• When and why to use aliases
• Best practices for readable queries

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✅ 1. Column Aliases

SELECT first_name AS name, salary * 12 AS annual_salary
FROM employees;

✅ Renames columns in the result set without altering the underlying schema.

📝 Notes:

• AS is optional in most databases: first_name AS name ≈ first_name name
• Use quotes or brackets if the alias contains spaces

SELECT salary * 12 AS "Annual Salary"
FROM employees;

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🧾 2. Table Aliases

SELECT e.first_name, d.name
FROM employees AS e
JOIN departments AS d ON e.department_id = d.id;

✅ Assigns a short name to a table—useful in joins and subqueries.

📝 Notes:

• Short aliases (like e, d, t1, t2) reduce query length
• Required in self-joins and correlated subqueries

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🔁 3. Aliases in Aggregates

SELECT department_id, COUNT(*) AS employee_count
FROM employees
GROUP BY department_id;

✅ Renames aggregate results for readable output.

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🧠 4. Aliases in Subqueries

SELECT * FROM (
  SELECT id, price * quantity AS total
  FROM sales
) AS revenue_report;

✅ Required to name derived tables and inline views.

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📘 Best Practices

✅ Recommended	❌ Avoid This
Use aliases for clarity and brevity	Using long or cryptic alias names
Alias aggregates and expressions	Leaving raw expressions in output
Use table aliases in multi-joins	Repeating full table names

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📌 Summary – Recap & Next Steps

SQL aliases improve readability, maintainability, and output formatting. They’re essential in complex queries involving joins, subqueries, and aggregations.

🔍 Key Takeaways:

• Column aliases rename output fields
• Table aliases simplify joins and subqueries
• Use AS for clarity, though it’s optional

⚙️ Real-World Relevance:
Used in reports, dashboards, APIs, and dynamic query builders.

➡️ Next: Explore SQL CASE WHEN for conditional output formatting.

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❓ FAQ – SQL Aliases

❓ What is an alias in SQL?

✅ A temporary name given to a column or table in a query.

❓ Do aliases affect the database schema?

✅ No. They only affect the query result.

❓ Is AS required for creating aliases?

❌ No. Most databases allow aliases without AS.

❓ Can I use spaces in alias names?

✅ Yes, if wrapped in quotes: AS "Annual Revenue"

❓ Why use table aliases?

✅ To shorten query length and make joins more readable.

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