Set Vs Select in T-SQL

Select will allow more than one records to to assigned to variable:

SELECT @var = singleColumn
FROM tab

Set either allow one record, or generate an error while the original value of variable remains unchanged:

SET @var =
( SELECT singleColumn
FROM tab
)


http://sqlblogcasts.com/blogs/tonyrogerson/archive/2006/05/18/449.aspx