if statement - SAS: update dataset if it exists, else create it -

i need update dataset mylib.dt_old using dataset dt_new, want first check if exists, otherwise error. in case not exist, want create dataset mylib.dt_old stores information contained in dt_new. tried following:

if (exist(mylib.dt_old))  do;   data   mylib.dt_old;   update mylib.dt_old  dt_new;   date var1 var2;    run; end; else do;   data mylib.dt_old;  set dt_new;   run; end; 

however error, when mylib.dt_old not exist

error: file mylib.dt_old.data not exist. 

and sas goes on executing else statement (creates dt_old copying dt_new).

instead if dt_old exist

   if (exist(mylib.dt_old))    --    180    error 180-322: statement not valid or used out of proper order. 

what doing wrong? ps: beginner in sas.

what you're trying qualify macro programming in sas, considered "advanced" topic.

the normal if-then control logic you're using sas considers data-step code, i.e. it's valid in data step. there "macro" language looks similar, distinguished % prefixes. here's how modified code might look:

%macro updater();     %if %sysfunc(exist(mylib.dt_old))      %then %do;         data   mylib.dt_old;             update mylib.dt_old  dt_new;             date var1 var2;          run;     %end;     %else %do;         data mylib.dt_old;             set dt_new;         run;     %end; %mend updater; %updater() 

while example sort-of straightforward, sas macro language counterintuitive (to me @ least). if you're beginner might idea find , read "into sas macros" online.