How can I prefix all column names in a T-SQL function?

Question

I have a table T with 2 columns C1 and C2

I want a function that returns T but after prefixing all column names with \"PREFIX_\".

The prefix is a dynamic str

Answer 1

This will do it even when you don't know the columns already.

declare @prefix varchar(20)
declare @sqltext nvarchar(500)
set @prefix = 'prefix_'

declare @columnnames varchar(500)

select @columnnames = coalesce(@columnnames, '')+',' +column_name + ' '+ @prefix+column_name 
from INFORMATION_SCHEMA.COLUMNS a where table_name = 't' and table_schema = 'dbo'

set @sqltext = 'select '+stuff(@columnnames,1,1,char(0))+' from t'

exec(@sqltext)

Answer 2

As its for a known number of columns you can construct the SQL string with the alias and exec() it;

declare @prefix varchar(32) = 'prefix_'
declare @sql    nvarchar(1024) 

set @sql = 'select C1 as [' + @prefix + 'C1], C2 as [' + @prefix + 'C2] from T'
exec(@sql)