There are two methods of creating alias name for a column
SELECT 100 as number
SELECT 100 number
Both result to 100 with column name number
You can use the keyword AS followed by alias name or use a space (But I prefer AS for better clarity and avoid mismatch in the result. See Missing comma and column alias for more information)
Did you know that in SQL Server the following will work same way as above?
For string value, except dot followed by alias, all other will work
SELECT 'SQL Server'name
SELECT 'SQL Server' 'name'
SELECT 'SQL Server'"name"
SELECT 'SQL Server'[name]
It should be noted that without space or AS keyword, SQL Server implicitly making succeeding alphabets/alphanumrics as column alias
So you should be aware of this especially the first example