"case when" in sql "then 1 else 0 end as" <-- what does this syntax mean?

[cdubs]

The below was prefaced by 

%let startdate = '01JAN1999'd;
%let elig_2010 = '31DEC2010'd;
....

Question 1 of 2: For above, why is there a 'd' after the date? Is this how data is typically stored?

Question 2 of 2: For below, I think its saying when svcdate >= 01JAN1999 but svcdate <= 31DEC2010, then do the subsequent thing. But I don't understand what "then 1 else 0 end as test_2010" means. Does that mean make the variable test_2010 into 1 if true, else not? Why is there an "end"?

proc sql; 
	create table hbsag_lab (rename=(enrolid=patient_id)) as
	select distinct enrolid, svcdate,
	case when &startdate. <=svcdate <= &elig_2010. then 1 else 0 end as test_2010

from clean_dataset (where=(lab_test=1));

quit;

[art297 · Accepted solution]

Your understanding is correct. As for the dates, quoting a date and then following it with a d converts the date to a SAS date, namely the number of days since January 1, 1960.

case statements, by definition, end with an end statement, followed by the variable name the selected/comuted values are assigned.

Art, CEO, AnalystFinder.com