Index usage problem..

Question

I got an requirement stating to get a max value of column b for given value for column a. Since to avoid a table scan, I created a composite Index on (a, b).
I tried with the query
select max(b) from table where a = invalue
Since the index is already been sorted the max(b) for value of a should be direct. But the explain plan for this query says, a range scan on the index and a sort and then the output of value.
But I like to have a single row fetch directly. Pls help me in modifying the query to get the max value directly without any scans.
Thanks
Suriya.

Answer 1

I'm not sure whether it is work, but you can try :
(1) Using single select statement
select x.b
from ( select b from table
where a = invalue
order by b desc
where rownum = 1;
OR
(2) PL/SQL program
begin
for c1rec in ( select b from table
where a = invalue
order by b desc ) loop
dbms_output.put_line(c1rec.b);
exit;
end loop;
end;
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