help: optimizer can't use index on Y to speed up select .. sum(X) ... group by Y

Using Oracle 7.1.3.3.6 (with rule based optimizing) on WindowsNT 3.5 I run in the following problem (simplified):

I have a table created by
  CREATE TABLE T1 ( KEY CHAR(1) NOT NULL, VALUE NUMBER NOT NULL ); indexed on the key-column with
  CREATE INDEX T1_01 ON T1 ( KEY ) Analyzing the query
  SELECT KEY,SUM(VALUE) FROM T1 GROUP BY KEY; i get the execution plan
  SORT GROUP BY
    TABLE ACCESS FULL T1 Since T1 is indexed on KEY, I'd expect the optimizer to avoid the  'SORT GROUP BY', but obviously it can't take advantage of the index.   

Investigating further I found that

     SELECT MIN(KEY) FROM T1 
          is planned
     SORT AGGREGATE
       INDEX RANGE SCAN T1_01
whereas
     SELECT MIN(KEY),MIN(KEY) FROM T1
          is planned
     SORT AGGREGATE
       TABLE ACCESS FULL T1

    SELECT KEY,COUNT(*) FROM T1 GROUP BY KEY           is planned
    SORT GROUP BY
      TABLE ACCESS FULL T1 The execution of the (more complex) original statement on a big table requires enormous amounts of temp-space for sorting, writes lots of redo-log and is very slow.
Of course I could do the task in PL/SQL with a cursor 'select key,value from t1 order by key'
computing the sum of values per key 'by hand', but since this kind of problem doesn't sound
uncommon I wonder, if there are other solutions.

So I have a few questions:

• am I missing something
• has anybody encountered/solved a similar problem
• is this behaviour a (known) bug/missing feature of the ruleOptimizer
• would it help to use the costOptimizer instead (with/without hints)
• will the behaviour change in Oracle >= 7.2

Any experiences/help/hints/suggestions are appreciated

Thanks in advance

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