-- Ausgabe der Ergebnisse
SET LONG 10000;
SET PAGESIZE 1000
SET LINESIZE 200
SELECT DBMS_SQLTUNE.report_tuning_task('my_sample_tuning_task') AS recommendations FROM dual;
SET PAGESIZE 24
RECOMMENDATIONS
--------------------------------------------------------------------------------
GENERAL INFORMATION SECTION
-------------------------------------------------------------------------------
Tuning Task Name : my_sample_tuning_task
Scope : COMPREHENSIVE
Time Limit(seconds): 60
Completion Status : COMPLETED
Started at : 05/06/2009 12:29:15
Completed at : 05/06/2009 12:29:19
-------------------------------------------------------------------------------
SQL ID : 0wrmfv2yvswx1
SQL Text: SELECT e.*, d.* FROM emp e JOIN dept d ON e.deptno = d.deptno
WHERE NVL(empno, '0') = :empno
-------------------------------------------------------------------------------
FINDINGS SECTION (2 findings)
-------------------------------------------------------------------------------
1- Statistics Finding
---------------------
Table "SCOTT"."EMP" and its indices were not analyzed.
Recommendation
--------------
Consider collecting optimizer statistics for this table and its indices.
execute dbms_stats.gather_table_stats(ownname => 'SCOTT', tabname =>
'EMP', estimate_percent => DBMS_STATS.AUTO_SAMPLE_SIZE,
method_opt => 'FOR ALL COLUMNS SIZE AUTO', cascade => TRUE)
Rationale
---------
The optimizer requires up-to-date statistics for the table and its indices
in order to select a good execution plan.
2- Restructure SQL finding (see plan 1 in explain plans section)
----------------------------------------------------------------
The predicate NVL("E"."EMPNO",0)=:B1 used at line ID 2 of the execution plan
contains an expression on indexed column "EMPNO". This expression prevents
the optimizer from selecting indices on table "SCOTT"."EMP".
Recommendation
--------------
Rewrite the predicate into an equivalent form to take advantage of
indices. Alternatively, create a function-based index on the expression.
Rationale
---------
The optimizer is unable to use an index if the predicate is an inequality
condition or if there is an expression or an implicit data type conversion
on the indexed column.
-------------------------------------------------------------------------------
EXPLAIN PLANS SECTION
-------------------------------------------------------------------------------
1- Original
-----------
Plan hash value: 1863486531
----------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
----------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 107 | 4 (0)| 00:00:01 |
| 1 | NESTED LOOPS | | 1 | 107 | 4 (0)| 00:00:01 |
| 2 | TABLE ACCESS FULL | EMP | 1 | 87 | 3 (0)| 00:00:01 |
| 3 | TABLE ACCESS BY INDEX ROWID| DEPT | 1 | 20 | 1 (0)| 00:00:01 |
| 4 | INDEX UNIQUE SCAN | PK_DEPT | 1 | | 0 (0)| 00:00:01 |
----------------------------------------------------------------------------------------
Note
-----
- dynamic sampling used for this statement