Aggregate function in native query (EJB 3.0)

Question

How do you run a aggregate function in a native query? I have a particular use case, for reporting purposes, where the result set is too large to fetch the actual CMP collection, thus I need to execute a native count/avg select. I want some thing like,
Integer totalRecords = (Integer)
       em.createNativeQuery("select count(*) from records").getSingleResult();

Answer 1

Oracle is intelligent enough to use index only if query result filtering is based on it and result set is less than 5% of the total data set.Sorry to be blunt but that 5% stuff is nonsense.
Here since the index column is not used in the WHERE clause, oracle performs full table scan.That's not true either. Under the right circumstances the optimizer can use the index, even without a WHERE clause in the query:
SQL> create table t as select * from dba_objects where object_type is not null;
Table created.
SQL> alter table t modify object_type not null;
Table altered.
SQL> create index t_idx on t(object_type);
Index created.
SQL> explain plan for
  2  select object_type, count(*) from t group by object_type;
Explained.
| Id  | Operation             | Name  | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT      |       |    44 |   396 |    60   (7)| 00:00:01 |
|   1 |  HASH GROUP BY        |       |    44 |   396 |    60   (7)| 00:00:01 |
|   2 |   INDEX FAST FULL SCAN| T_IDX | 72474 |   636K|    57   (2)| 00:00:01 |
-------------------------------------------------------------------------------With the OP's query, it (apparently) can not be satisfied by using only the index.
WHERE TO_CHAR(COL) = TO_CHAR(COL)I don't even know what this means. Usually if you perform a function on an indexed column, the optimizer will not use the index (unless of course it's an fbi).