SQL | Aliases

In SQL, aliases are temporary names assigned to columns or tables to improve readability and simplify complex queries. It does not change the actual table or column name in the database—it's just for that one query.

It is used when the name of a column or table is used other than its original name, but the modified name is only temporary. Aliases help simplify long column names, improve query clarity, and are particularly useful in queries involving multiple tables or aggregated data.

• Makes long or complex names more readable
• Helps simplify joins and subqueries
• Improves clarity in result sets
• Avoids naming conflicts in multi-table operations

There are two types of aliases in SQL:

• Column Aliases: Temporary names for columns in the result set.
• Table Aliases: Temporary names for tables used within a query.

Example of SQL Aliases

We will use the following Customer table to demonstrate all SQL alias concepts. This table contains customer information such as ID, name, country, age, and phone number.

CREATE TABLE Customer (
    CustomerID INT PRIMARY KEY,
    CustomerName VARCHAR(50),
    LastName VARCHAR(50),
    Country VARCHAR(50),
    Age INT,
    Phone VARCHAR(15)
);

-- Inserting sample data into the Customer table
INSERT INTO Customer (CustomerID, CustomerName, LastName, Country, Age, Phone)
VALUES 
(1, 'Shubham', 'Thakur', 'India', 23, '9876543210'),
(2, 'Aman', 'Chopra', 'Australia', 21, '9876543211'),
(3, 'Naveen', 'Tulasi', 'Sri Lanka', 24, '9876543212'),
(4, 'Aditya', 'Arpan', 'Austria', 21, '9876543213'),
(5, 'Nishant', 'Jain', 'Spain', 22, '9876543214');

Output:

1. Column Aliases

A column alias is used to rename a column just for the output of a query. They are useful when:

• Displaying aggregate data
• Making results more readable
• Performing calculations

Syntax:

SELECT column_name AS alias_name

FROM table_name;

The following table explains the arguments in detail:

• column_name: The column name can be defined as the column on which we are going to create an alias name.
• alias_name: It can be defined as a temporary name that we are going to assign for the column or table. 
• AS: It is optional. If you have not specified it, there is no effect on the query execution. 

Example 1: Column Alias for Renaming a Column

To fetch the CustomerID and rename it as id in the result set

SELECT CustomerID AS id
FROM Customer;

Output:

2. Table Aliases

A table alias is used when you want to give a table a temporary name for the duration of a query. Table aliases are especially helpful in JOIN operations to simplify queries, particularly when the same table is referenced multiple times (like in self-joins).

Example 2: Table Alias for Joining Tables

We want to join the Customer table with itself to find customers who have the same country and are aged 21. We'll use table aliases for each instance of the Customer table.

Query:

SELECT c1.CustomerName, c1.Country
FROM Customer AS c1, Customer AS c2
WHERE c1.Age = c2.Age AND c1.Country = c2.Country;

Output:

Here, c1 and c2 are aliases for two instances of the Customer table.

Combining Column and Table Aliases

We want to fetch customers who are aged 21 or older and rename the columns for better clarity. We'll use both table and column aliases.

Query:

SELECT c.CustomerName AS Name, c.Country AS Location
FROM Customer AS c
WHERE c.Age >= 21;

Output:

Practical Uses of SQL Aliases

• Better Readability: Makes complex names shorter and easier to understand.
• Simplifies Queries: Reduces repetition, especially in joins.
• Clear Output: Renames columns for more meaningful results.
• Avoids Conflicts: Prevents naming clashes in multi-table queries.