SAS Datetime Proc SQL - sql

Question

Hello I was wondering how would you write this code in a PROC SQL vs the data step I wrote below. I am trying to reduce the code, the data is initially in a text file unfortunately the datetime when changed to a CHAR(import wizard) is a length of 9 vs 8(computed column) which is the default, hence why i change it in the first data step. I eventually get the results I want but I would like to see if SQL could provide a more efficient solution.
data WORK.CNE_RESI;
SET WORK.cneres_41;
FORMAT RPTDATE_2 $CHAR9.;
IF rptdate = '1/5/2015' THEN RPTDATE_2 = '1/9/2015';
ELSE IF RPTDATE_2 = "" THEN RPTDATE_2=rptdate ;
RUN;
data WORK.CNE_RESI_2;
SET WORK.CNE_RESI;
FORMAT RPTDATE_3 MMDDYY10.;
RPTDATE = input(RPTDATE_2, MMDDYY10.);
RUN;

Answer 1

Not sure if this is the right way to do it but I had a go.
%let olddate = 1/5/2015;
%let newdate = 1/9/2015;
proc sql;
create table WORK.CNE_RESI_2 as
select a.*,
case when rptdate = "&olddate" then "&newdate"
else rptdate
end as RPTDATE_2 format=$char9.,
input(case when rptdate = "&olddate" then "&newdate"
else rptdate
end,mmddyy10.) as RPTDATE_3 format=mmddyy10.
from WORK.cneres_41 a;
quit;
Of course if you didn't actually need the variable rptdate_2 and were just using that to change format then this should work.
proc sql;
create table WORK.CNE_RESI_2 as
select a.*,
input(case when rptdate = "&olddate" then "&newdate"
else rptdate
end,mmddyy10.) as RPTDATE_3 format=mmddyy10.
from WORK.cneres_41 a;
quit;

Answer 2

Your ultimate question is:
I eventually get the results I want but I would like to see if SQL
could provide a more efficient solution.
The reason that your DATA steps seem inefficient is that you make two complete passes over the data. There's no reason for that in this case, and a single DATA step is likely to be at least as efficient as SQL for your example. Also, placing the format statement above the set statement will redefine the length of rptdate without the need for an intermediate variable. With these thoughts in mind, your two DATA steps could be more efficiently written as:
data WORK.CNE_RESI;
format rptdate $char10. rptdate_n mmddyy10.;
set WORK.cneres_41;
if rptdate = '1/05/2015' then rptdate = '1/09/2015';
rptdate_n = input(rptdate, ?? MMDDYY10.);
run;