Is 'calculated' a reserved keyword in PROC SQL for alias usage?

In PROC SQL, the term 'calculated' is indeed a reserved keyword when used in the context of referencing an alias that has been created within the same SELECT statement. This keyword is particularly useful when users need to refer to a calculated value derived from an expression in the SELECT statement, especially if that calculation is needed in a subsequent part of the same query, such as in the WHERE or HAVING clause.

Using 'calculated' makes it clear to SAS that you are referring to an alias defined in the current step rather than trying to re-compute the expression. This ensures clarity and can enhance performance since it avoids recalculating the value. Therefore, whenever you create an alias for a calculated field, incorporating the 'calculated' keyword is essential to properly reference that alias within the same context.

Other options suggest varying degrees of permissiveness regarding the use of the keyword, but the necessity of 'calculated' for proper syntax and functionality in specific situations stands firm. Thus, understanding its role consolidates the fundamental practices of writing efficient PROC SQL statements.