SQL Aliases are temporary names for tables or columns in SQL queries. They make tables and column names more readable and reduce query length. Aliases are created using the AS keyword.

Syntax
SELECT column_name AS alias_name FROM table_name AS alias_name

SQL aliases are not necessary for every SQL query. However, they are commonly used when working with multiple tables, especially in SQL JOIN queries. Using aliases can help avoid the need to repeatedly use the full table name before column names, which can make the queries more readable and easier to write.
Using ‘AS’ keywords is not necessary to create an Alias function.

Aliases using the AS keyword

SELECT u.user_id AS id, u.user_name AS name, a.city
FROM users AS u
JOIN address AS a ON a.user_id_fk = u.user_id

Aliases not using the AS keyword

SELECT u.user_id id, u.user_name name, a.city
FROM users u
JOIN address a ON a.user_id_fk = u.user_id