How to merge/set two dataset

[JacksonWang]

I have two dataset, I want to do like that:

Data 1

ID	Y
1	10
2	20

Data 2

ID	Y
1	100
1	200
2	300
3	100
4	500

Wanted Data 3 (based on data 1 ID)

ID	Y
1	10
1	100
1	200
2	20
2	300

I used the code:

data data3;
   merge data1(in=a) data2;
   by id;
   if a=1;
run;

But the y of data 1 with same ID will be overwrite, so how should I create data3?

Thank you very much.

[Patrick · Accepted solution]

It appears you don't want to merge but to interleave the data sets - but then only keep rows with id's that exist in your first source table.

data have1;
  input id y$;
datalines;
1 10
2 20
;
data have2;
  input id y$;
datalines;
1 100
1 200
2 300
3 100
4 500
;

data want;
  set have1 (in=in1) have2;
  by id;
  retain keep_id;
  if first.id then keep_id=in1;
  if keep_id=1;
  drop keep_id;
run;

proc print data=want;
run;