Do it in proc sql - sas

Question

How to do below codes in proc sql.
Two proc statement and one merge given below.
proc sort data=new out=new1 nodupkey;
by id;
where roll=100;
run;
proc sort data new2 out =new4 nodupkey
by id;
where roll=100;
run;
data score;
merge new4 (in=a) new1;
by id;
if a;
run;

Answer 1

The merge you show is equivalent to SQL left-join. You want all the rows from "new2" and ignore all the rows from "new" that don't have a common id. The uniqueness of the id (per the pre-sorts) further supports a left-join equivalence.
Proc SQL;
select new.*, new2.*
from new2
left join new on new.id = new2.id
where roll=100
order by id;
quit;
For the scenario of atypical data where there is many:many ids in the merge, the left-join is not equivalent.
I did leave out the NODUPKEY equivalent. Presuming option EQUALS is in effect, the selection of a groups first row would be equivalent. The undocumented MONOTONIC() function can be used to apply a default row order to a sub-query, which can then be used in a by group having expression.
data LEFT;
input id x1 x2 x3;
datalines;
1 1 1 1
1 2 2 2
1 3 3 3
2 1 1 1
2 2 2 2
3 3 3 3
4 4 4 4
5 5 5 5
;
run;
data RIGHT;
input id y1 y2 y3 x1;
datalines;
1 1 1 1 11
2 1 1 1 22
3 1 2 3 4
3 2 3 4 5
3 3 4 5 6
4 1 1 1 44
6 6 6 6 6
;
run;
proc sql;
select
LEFT.id
, coalesce(RIGHT.x1,LEFT.x1) as x1
, LEFT.x2
, LEFT.x3
, RIGHT.y1
, RIGHT.y2
, RIGHT.y3
from
(
select * from (select monotonic() as _seq_, * from LEFT) group by id having _seq_ = min(_seq_)
)
as LEFT
left join
(
select * from (select monotonic() as _seq_, * from RIGHT) group by id having _seq_ = min(_seq_)
)
as RIGHT
on
LEFT.id = RIGHT.id
;
I feel the need to reiterate that SQL left join is not always the same a merge, and SQL does not have common variable 'overlaying' that is implicit in DATA Step. When LEFT and RIGHT collide on non-key variables, you need to select a coalescence of the common variables into a new like-named variable in the output.