List of data sets in a library

[Ronein]

Hello

Lets say that I  want to find all data sets in library R_R that start with name "ALERTSNEG_"

For example: ALERTSNEG_202401 , ALERTSNEG_202402, ALERTSNEG_202403 and so on

Lets say that I want to create a macro var that concatenated these data sets names.

My question:

what is the target of writing the code : %let memlist=_null_;

The code can also run without it.

Can anyone explain what is the benefit of this code?

proc sql noprint ;
%let memlist=_null_;
select catx('.',libname,memname)
    into :memlist separated by ' '
from dictionary.members 
where libname='R_R'
      and (memname like 'ALERTSNEG_%')
  ;
quit;
%put &memlist;

[PeterClemmensen]

Probably just to ensure that memlist does not contain anything from the previous run of the code. It works perfectly fine without it though. 

[Kurt_Bremser · Accepted solution]

If there's no dataset satisfying the WHERE requirement, PROC SQL would not create the macro variable, causing ERRORs later on when you use it. The %LET avoids this.

[Ronein]

Is it equivalent to write 

%let memlist=_null_;

before the proc sql?

%let memlist=_null_;
proc sql noprint ;
select catx('.',libname,memname)
    into :memlist separated by ' '
from dictionary.members 
where libname='R_R'
      and (memname like 'ALERTSNEG_%')
  ;
quit;
%put &memlist;

[Kurt_Bremser]

Answer these two questions:
- When are macro statements executed/resolved?
- When does the SQL procedure execute statements, interactively when encountered, or all at once when QUIT; is parsed?