SQL Aliases

SQL aliases are used to give a table or a column in a table a temporary name. This can be helpful for simplifying queries, making the output more readable, and dealing with tables or columns that have complex or lengthy names.

Column Aliases

A column alias allows you to rename a column for the duration of a query. This is done using the AS keyword.

Example:

Suppose you have a table named employees with the following columns: emp_id, first_name, last_name, and salary.

SELECT emp_id AS ID, first_name AS "First Name", last_name AS "Last Name", salary AS "Monthly Salary"
FROM employees;

Output:

Table Aliases

A table alias allows you to rename a table for the duration of a query. This is particularly useful in complex queries involving multiple tables, especially in JOIN operations.

Example:

Suppose you have two tables: employees and departments. The employees table has columns emp_id, first_name, last_name, dept_id, and the departments table has columns dept_id and dept_name.

SELECT e.emp_id, e.first_name, e.last_name, d.dept_name
FROM employees AS e
JOIN departments AS d
ON e.dept_id = d.dept_id;

Output:

Combined Example

You can combine column and table aliases to simplify your query even further.

Example:

SELECT e.emp_id AS ID, e.first_name AS "First Name", e.last_name AS "Last Name", d.dept_name AS "Department"
FROM employees AS e
JOIN departments AS d
ON e.dept_id = d.dept_id;

Output:

In this example, the table employees is aliased as e, the table departments is aliased as d, and columns are also given more readable names.