MySQL Alias

The MySQL alias is a temporary name assigned to a column, table, or subquery result in a SQL query. Aliases are useful for making query results more readable, for renaming columns, and for simplifying the use of lengthy table or column names. You can assign aliases using the AS keyword or without it.

Here are some common uses of aliases in MySQL:

1. Column Alias: You can use aliases to rename the columns in your query results. This is particularly useful when you want to change the name of a column to make the output more meaningful.

   SELECT first_name AS "First Name", last_name AS "Last Name"
   FROM employees;

2. Table Alias: When you have complex queries involving multiple tables, you can assign aliases to those tables to make the query more readable and to avoid naming conflicts between columns.

   SELECT o.order_id, c.customer_name
   FROM orders AS o
   JOIN customers AS c ON o.customer_id = c.customer_id;

3. Alias for Expressions: You can also use aliases for expressions, calculations, or subqueries to make your query more concise.

   SELECT product_name, (unit_price * quantity) AS total_price
   FROM order_details;

4. Alias for Subqueries: If you use a subquery within your query, you can assign an alias to the result of the subquery. This can be helpful for referencing the subquery in the outer query.

   SELECT customer_name, (SELECT AVG(order_total) FROM orders) AS avg_order_total
   FROM customers;

When defining aliases, you can use double quotation marks to enclose the alias if it contains spaces or special characters, as shown in the first example. However, this is optional for column and table aliases that follow standard naming conventions.

Aliases are valuable for improving the readability and maintainability of your SQL queries and for making the output more informative.