How to use a value that comes from a different table? - sas

Question

I created a dataset to calculate a threshold:
Data black;
Set blue;
Lower=p20-2;
Upper=p20+2;
Run;
I would like to use this value the output is something like:
Variables n lower upper
Val 123 -0.2 0.1
I would like to use upper and lower as thresholds:
Proc sql;
Create table one as
Select * from two
Where (Val < upper and Val > lower)
;quit;
Upper and lower should come from black, while Val should come from two.
two looks like
ID Val
42 1471
32 1742
74 4819
...
How can I include the threshold in my dataset in order to filter values from two?
A possible solution could be adding lower value and upper value to two columns, but I do know how to assign the values to these columns.

Answer 1

If your bounds are static for all rows, you can read them into macro variables and reference them in your SQL query.
data black;
set blue;
Lower=p20-2;
Upper=p20+2;
/* Save the value of lower/upper to macro variables &lower and &upper */
call symputx('lower', lower);
call symputx('upper', upper);
run;
proc sql;
create table one as
select * from two
where &lower. < Val < &upper.
;
quit;
If each ID has a specific threshold value, you can use a hash table to look up each value by its key. Hash tables are very efficient in SAS and are a great way of doing lookups of small tables in a big table.
data two;
set one;
if(_N_ = 1) then do;
dcl hash h(dataset: 'blue');
h.defineKey('id');
h.defineData('lower', 'upper');
h.defineDone();
/* Initialize lower/upper to missing */
call missing(lower, upper);
end;
/* Take the ID for the current row in the and look it up in hash table.
If there is a match, return the value of lower/upper for that ID */
rc = h.Find();
/* Only output if the ID is between its threshold */
if(&lower. < Val < &upper.);
drop rc;
run;
If you prefer to use SQL, you can manipulate the SQL optimizer to force a hash join with the undocumented magic=103 option. This sometimes can be more efficient with joins on smaller tables.
proc sql magic=103;
create table two as
select t1.*
from one as t1
LEFT JOIN
black as t2
ON t1.id = t2.id
where t2.lower < t1.val < t2.upper
;
quit;