SAS merge question

[Niugg2010]

When I run below code. I found only the first record of a column is populated by 'A' and other records are keeping blank for a column. Does someone help me to understand the reason? Thanks

data a;
a=' ';
b=1;
do i=1 to 10;
output;
end;
run;
data b;
a='A';
b=1;
run;
proc sort data=a; by b;run;
proc sort data=b; by b; run;
data c;
merge a b;
by b;
run;

[Tom · Accepted solution]

SAS copies the values from a dataset only once.  So for the first observation it reads variables A and B from dataset WORK.A and then overwrites the values read with the values read from WORK.B.  But on the other observation there are no more records to read from WORK.B so the values read from WORK.A are not overwritten. 

If you want to only keep the value of A from WORK.B then drop the variable from WORK.A.  You could do it in the step with the MERGE by using the DROP= dataset option.

data c;
  merge a(drop=a) b;
  by b;
run;

[PhilC]

What did you expect the output to be?  Perhaps we can help you better if we see how you might be thinking.  We can focus on what part of your hypothesis is incorrect.

[Niugg2010]

Thanks a lot. I thought sas read datasets into Program Data Vector(PDV). each time dataset b will overwrite dataset a. so a column should be all populated finally.