Hi Ashok, thanks for your question. If you are using the fedsql.execDirect action, you can use the standard SQL joins like inner, left, right, full. For example:

proc cas;
fedsql.execDirect/
query=
"
select *
from TABLE1 a left join TABLE2 b
on a.VAR1 = b.VAR1
"
casout={name="TABLE3", replace=True};
quit;

You can also use the data step merge syntax inside Proc CAS, for example:
proc cas;
dataStep.runCode /
code="
data casuser.merged;
merge casuser.test1 casuser.test2;
by var1;
run;
";
quit;