PROC SQL allows a subquery (contained in parentheses) at any point in an expression where a simple column value or constant can be used. In this case, a subquery must return a single value, that is, ...

The keyword CASE is always reserved; its use in the CASE expression (an SQL2 feature) precludes its use as a column name. If you have a column named CASE in a table and you want to specify it in a ...