HPL/SQL does not allow variables in update statements

DECLARE
val_to_update varchar(10);
BEGIN
val_to_update := 'one';
FOR REC in (select a,b from test1 where a = val_to_update) LOOP
dbms_output.put_line (rec.a);
dbms_output.put_line (rec.b);
END LOOP;
update test1 set b = 'another'
where a = val_to_update;
end;

DECLARE
val_to_update STRING;
BEGIN
val_to_update := 'one';
FOR REC in (select a,b from test where a = val_to_update) LOOP
print (rec.a);
print (rec.b);
END LOOP;
update test set b = 'another test'
where a = val_to_update;
end;
/
ERROR : FAILED: SemanticException [Error 10004]: Line 2:14 Invalid table alias or column reference 'val_to_update': (possible column names are: a, b)
org.apache.hadoop.hive.ql.parse.SemanticException: Line 2:14 Invalid table alias or column reference 'val_to_update': (possible column names are: a, b)
at org.apache.hadoop.hive.ql.parse.SemanticAnalyzer.genAllExprNodeDesc(SemanticAnalyzer.java:13636)
at org.apache.hadoop.hive.ql.parse.SemanticAnalyzer.genExprNodeDesc(SemanticAnalyzer.java:13575)
...

DECLARE
val_to_update STRING;
BEGIN
val_to_update := 'one';
FOR REC in (select a,b from test where a = val_to_update) LOOP
print (rec.a);
print (rec.b);
END LOOP;
select * from test
where a = val_to_update;
end;
/