since there are only two variables in table B. you merge table A and B together. It is very easy.
data C;
merge A B(rename=(x=xb y=yb));
xx = (x-bx)^2;
yy = (y-by)^2;
run;

If your case is more complicated, send me the detail. I hope this will be helpful.

还可以这样
data a;
infile "C:\360Downloads\test4.csv" missover dsd firstobs =2;
input id m $ n $ x y;
run;
data b;
input x1 y1;
cards;
0.123 0.456
;
run;
data union;
if _n_ =1 then set b;
set a;
run;