DateTime trouble in SAS - sas

Question

I have a big database. There's a contract start date there. The problem is that in some time ago, several values had been imported there as a datetime format while the rest are just date9. In result now some sql queries or data queries shows weird results due to difference in seeing the "numbers" stored behind the contract start date.
Like when I want to get max(contract_start_date) (via sql, for example) I will get *************** instead of normal results.
My question is how can I unify this format difference? What I would like in the end is to make a new variable with unified format and then replace the existing contract start date with new one.

Answer 1

%let d_breakpoint=%sysfunc(putn('31dec2015'D, 13. -L));
%put &d_breakpoint;
%put %sysfunc(putn(&d_breakpoint, DATETIME. -L));
data indata;
format contract_start_date date9.;
do i=0 to 40;
contract_start_date = i*5000;
output;
end;
drop i;
run;
proc sql;
alter table indata add d_contract_start num format=date9.
;
update indata
set d_contract_start= case when contract_start_date > &d_breakpoint then contract_start_date/(24*60*60)
else contract_start_date end
;
quit;
proc sql;
select
min(d_contract_start) format=date9. as min
, max(d_contract_start) format=date9. as max
from indata
;
quit;
The variable has only one format, but one part of VALUES of that variable stored in table is not corresponding to that format - if the format is for DATE values (date as a number of days since 1jan1960) but some records store DATETIME values (number of seconds since midnight 1jan1960), the results are incorrect.
So you need to modify values to be of just one type - DATE or DATETIME.
The code above will change it to DATE values.
The idea is to define a breakpoint value - values above that will be treated as DATETIME values, the rest will be considered DATE values and will be kept like that.
In my example I've choosen DATE value of 31dec2015 (which is 20453) to be the breakpoint. So this represents 31dec2015 as DATE, while 01JAN60:05:40:53 as DATETIME.
Values below 20453 are considered DATE values, values above 20453 considered DATETIME values.