sas宏(3)理解符号表(全局宏与局部宏解析)，宏条件运算符,在宏中进行运算

Understanding the  Global Macro Symbol Table

　　Detail

　　　　•The macro processor creates the global macro symbol table at the start of a SAS session.

　　Four ways to create add macro to Global Macro Table

　　　　• Create the macro variable in open code.

　　　　• List the macro variable on a %GLOBAL(default value is null) statement in the macro program in which it is defined.

　　　　• Create the macro variable in a DATA step with CALL SYMPUTX when the global symbol table is specified.

　　　　• Define a global macro variable with the INTO clause on the PROC SQL SELECT statement.

　　Where and When they can be used?

　　　　You can reference global macro variables throughout the SAS session in which they are created. They can be referenced from open code and from inside macro programs.

　　EXAMPLE　

options symbolgen mprint;
/*reference in macro program*/
%let subset=Software;
%macro makeds;
  data temp;
    set books.ytdsales(where=(section=“&subset”));
    attrib qtrsold label='Quarter of Sale';
    qtrsold=qtr(datesold);
  run;
%mend makeds;
%makeds
/*reference in open code*/ 
proc tabulate data=temp;
  title “Book Sales Report Produced &sysdate9”;
  class qtrsold;
  var saleprice listprice;
  tables qtrsold all,
         (saleprice listprice)*(n*f=6. sum*f=dollar12.2) /
         box=“Section: &subset”;
  keylabel all='** Total **';
run;

Understanding the Local Macro Symbol Table

　　Detail

　　　　•If your macro program creates macro variables and does not specify them as global macro variables,  the macro processor usually creates a local macro symbol table when that macro program executes,When the macro program finishes, the macro processor deletes the associated local macro symbol table.

　　Four ways to create add macro to Global Macro Table

　　　　• Create the macro variable in open code.

　　　　• List the macro variable on a %GLOBAL statement in the macro program in which it is defined.

　　　　• Create the macro variable in a DATA step with CALL SYMPUTX when the global symbol table is specified.

　　　　• Define a global macro variable with the INTO clause on the PROC SQL SELECT statement.

　　Where and When they can be used?

　　　　You can reference global macro variables throughout the SAS session in which they are created. They can be referenced from open code and from inside macro programs.

　　How to Delete

　　　　A global macro variable can be deleted by macro language statement %SYMDEL

　　EXAMPLE