Using Aliases ( AS ) in SQL

Aliases are temporary names that you assign to columns or tables to make your SQL queries more readable and clean . They don’t change the original names in the database — they only exist within the context of that query .

🔧 Syntax

👉 For Column Aliases:

SELECT column_name AS alias_name 
 FROM table_name;  

👉 For Table Aliases:

SELECT t.column_name 
 FROM table_name AS t;  

🎓 Why Use Aliases?

• Make column names more descriptive
• Simplify long or complex table names
• Improve readability in joins and subqueries
• Format output for reports

🧪 Our Sample Table: students

id	name	age	course	marks
1	Rahul Sharma	21	Advanced SQL	90.00
2	Anjali Kapoor	22	Advanced SQL	91.75
3	Vikas Gupta	24	Advanced SQL	91.00
4	Riya Jain	20	Python	92.50
5	Aman Verma	24	Advanced SQL	76.00

📘 Example 1: Column Alias

SELECT 
 name AS student_name, 
 marks AS obtained_marks 
FROM students;  

Output:

student_name	obtained_marks
Rahul Sharma	90.00
Anjali Kapoor	91.75
...	...

📘 Example 2: Table Alias

SELECT s.name, s.course FROM students AS s;  

✅ s is a short alias for the students table.

📘 Example 3: Use in Aggregation

SELECT course, AVG (marks) AS average_score 
 FROM students GROUP BY course;  

✅ average_score is easier to understand than AVG(marks) in the output.

📘 Example 4: Alias Without AS

Using AS is optional. You can also write:

SELECT name student_name, marks obtained_marks 
 FROM students;  

But using AS is recommended for clarity.

⚠️ Alias Rules

Rule	Example
Alias with spaces? Use quotes	AS "Total Marks"
Avoid using SQL keywords as aliases	AS total (OK), not AS select
Case sensitivity depends on DB system	"Name" vs name

🧠 Best Practices

• Always use aliases in joins or subqueries .
• Use clear, descriptive names (avoid x , y unless in simple examples).
• Prefer AS for readability.

✅ Summary

Feature	Example	Purpose
Column Alias	marks AS total_marks	Rename output column
Table Alias	students AS s	Shorten table name
Optional AS	marks total	Still valid but less readable

🎯 Real Life Tip: When writing reports , dashboards , or complex joins , aliases make queries much more understandable and professional.