- A column alias provides a way to create a clean or more descriptive header for a results set.
- A column alias cannot be used in a SELECT, WHERE, GROUP BY or HAVING clause due to the order of execution. You must refer to the original column name.
In the previous example, we created a new column that was a calculated value. The problem is that the column header is now population / SurfaceArea. However, we can rename the column header to something cleaner by creating a column alias. Look at the code snippet below.
SELECT name, population / SurfaceArea
AS “People per square mile”
We used the AS keyword then in quotes we put the new column alias of “People per square mile.” Which changes the column header as seen show below.