Option 1

Unfortunately, SQL Server does not have an easy function to generate a comma-separated list, you will have to implement FOR XML PATH with the STUFF command to get the list.

For example:

SELECT STUFF((SELECT TOP 3 ', ' + COLUMN_NAME
       FROM INFORMATION_SCHEMA.COLUMNS
       FOR XML PATH('')), 1, 1, '') COLLATE DATABASE_DEFAULT

This example will return the first three rows from the COLUMNS table, in the following format:

AgencyName, AssetNo, ContractorID

If COLLATE DATABASE_DEFAULT is used the result may become truncated when using SSMS. Fix this by changing the SSMS setting Tools | Options... | Query Results | SQL Server | Results to Text | Maximum number of characters displayed in each column: to 8192. Then restart SSMS.

Option 2

The COALESCE option only works for variable output.

DECLARE @Names VARCHAR(8000) 
SELECT TOP 3 @Names = COALESCE(@Names + ', ', '') + COLUMN_NAME 
FROM INFORMATION_SCHEMA.COLUMNS

PRINT @Names

This example will return the first three columns from the COLUMNS table, in the following format:

AgencyName, AssetNo, ContractorID