> For the complete documentation index, see [llms.txt](https://courses.parottasalna.com/database-engineering/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://courses.parottasalna.com/database-engineering/querying-data/column-aliases.md). # Column Aliases > 📌 Note: This tutorial uses the dvdrental database. If you dont have the dvdrental, please go through this ### What are Column Aliases ? A column alias allows you to assign a column or an expression in the select list of a `SELECT` statement a temporary name. The column alias exists temporarily during the execution of the query. The following illustrates the syntax of using a column alias ```sql SELECT column_name AS alias_name FROM table_name; ``` In this syntax, the `column_name` is assigned an alias `alias_name`. The `AS` keyword is optional so you can omit it like this, ```sql SELECT column_name alias_name FROM table_name; ``` The main purpose of column aliases is to make the headings of the output of a query more meaningful. ### 1. Assigning a column alias to a column example The following query returns the first names and last names of first 5 customers from the `customer` table ```sql SELECT first_name, last_name FROM customer LIMIT 5; ```

If you want to rename the `last_name` heading, you can assign it a new name using a column alias like this ```sql SELECT first_name, last_name AS surname FROM customer LIMIT 5; ```

This query assigned the `surname` as the alias of the `last_name` column Or you can make it shorter by removing the `AS` keyword as follows, ```sql SELECT first_name, last_name surname FROM customer LIMIT 5; ```

### 2. Assigning a column alias to an expression example The following query returns the full names of first 5 customers. It constructs the full name by concatenating the first name, space, and the last name ```sql SELECT first_name || ' ' || last_name FROM customer LIMIT 5; ``` Note that in PostgreSQL, you use the `||` as the concatenating operator that concatenates one or more strings into a single string.

As you can see clearly from the output, the heading of the column is not meaningful `?column?` . To fix this, you can assign the expression `first_name || ' ' || last_name` a column alias e.g., `full_name` ```sql SELECT first_name || ' ' || last_name AS full_name FROM customer LIMIT 5; ```

### 3. Column aliases that contain spaces If a column alias contains one or more spaces, you need to surround it with double quotes like this ```sql column_name AS "column alias" ``` For example, ```sql SELECT first_name || ' ' || last_name "full name" FROM customer LIMIT 5; ```