The global symbol table is
created during the initialization of a SAS session or noninteractive execution
initialized with automatic or system-defined macro variables
deleted at the end of the session.
Macro variables in the global symbol table
are available anytime during the session
can be created by your program
have values that can be changed during the session (except some automatic macro variables)
cannot be removed once they are created (they can be assigned a null value).
A local symbol table is
created when a macro with a parameter list is called or a request is made to create a local variable during macro execution
deleted when the macro finishes execution.
The local symbol table contains macro variables that can be
created and initialized at macro invocation (parameters)
created during macro execution
updated during macro execution
referenced anywhere within the macro.