Which clause is used to create macro variables in a select statement in PROC SQL?

The use of the %MACRO clause in PROC SQL is essential for creating macro variables within a SELECT statement. This macro capability allows for dynamic and reusable code, enabling users to define a sequence of instructions or variables that can be executed later within the SAS environment. When you use %MACRO, you are essentially defining a macro that can encapsulate logic or variable definitions, which can then be executed or referenced throughout your SAS code.

In the context of PROC SQL, while other options might seem related to macro functionalities, only %MACRO serves as the proper definition tool for creating those macro variables. Each macro can include parameters, and when a SELECT statement is executed within the macro, it can dynamically assign values to macro variables based on the results of the query. This enhances the efficiency and modularity of SAS programming, allowing for cleaner and more maintainable code.

Understanding the use of %MACRO is crucial for anyone looking to perform advanced data manipulation and automation in clinical trials analysis using SAS.