SQL tuning problem

Question

I have a request:

select count(1) CNT
from file_load_params a
where a.doc_type = (select b.doc_type
                    from file_load_header b
                    where b.indicator = 'XELFASI')
 order by a.line_no

What is the plan of explanation:

-----------------------------------------------------------------------------------------------------
| Id  | Operation                     | Name                | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT              |                     |     1 |     7 |     3   (0)| 00:00:01 |
|   1 |  SORT AGGREGATE               |                     |     1 |     7 |            |          |
|*  2 |   TABLE ACCESS FULL           | FILE_LOAD_PARAMS    |    15 |   105 |     2   (0)| 00:00:01 |
|   3 |    TABLE ACCESS BY INDEX ROWID| FILE_LOAD_HEADER    |     1 |    12 |     1   (0)| 00:00:01 |
|*  4 |     INDEX UNIQUE SCAN         | FILE_LOAD_HEADER_UK |     1 |       |     0   (0)| 00:00:01 |
-----------------------------------------------------------------------------------------------------

I thought I could optimize this query and write it:

select count(1) CNT
from file_load_params a,file_load_header b
where  b.indicator = 'XELFASI'
and a.doc_type = b.doc_type
order by a.line_no

His plan of explanation:

-----------------------------------------------------------------------------------------------------
| Id  | Operation                     | Name                | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT              |                     |     1 |    19 |     3   (0)| 00:00:01 |
|   1 |  SORT AGGREGATE               |                     |     1 |    19 |            |          |
|   2 |   NESTED LOOPS                |                     |    15 |   285 |     3   (0)| 00:00:01 |
|   3 |    TABLE ACCESS BY INDEX ROWID| FILE_LOAD_HEADER    |     1 |    12 |     1   (0)| 00:00:01 |
|*  4 |     INDEX UNIQUE SCAN         | FILE_LOAD_HEADER_UK |     1 |       |     0   (0)| 00:00:01 |
|*  5 |    TABLE ACCESS FULL          | FILE_LOAD_PARAMS    |    15 |   105 |     2   (0)| 00:00:01 |
-----------------------------------------------------------------------------------------------------

It's good? I think not, but I was expecting a better result ... Do you have an idea?

Answer 1

One of the possible optimizations that I see from your plan of explanation is

TABLE ACCESS FULL           | FILE_LOAD_PARAMS  

This seems to indicate that the table file_load_paramsmay not have an index ondoc_type

If so, you can add an index for doc_type. If you already have indexes, can you place a table schema forfile_load_params

Answer 2

, . ?

ORDER BY. COUNT, .

Answer 3

The result does not match for the two queries. The IN statement also automatically applies DISTINCT to the internal query. And in this case, this is probably not the key you are joining (if so, make it a unique key), so it cannot be optimized.

With regard to the query optimization, how InSane says, add the index Doc_TypeinFILE_LOAD_PARAMS