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EXPLAIN PLAN FOR in oracle

jaya kemmannu
Ranch Hand

Joined: Sep 23, 2011
Posts: 84

Hi,

Can anyone explain use of the below query :

query : EXPLAIN PLAN FOR delete from x_table where x_column='60'; and its output is

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
Plan hash value: 4285998136

--------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------------------------------
| 0 | DELETE STATEMENT | | 1 | 17 | 2 (0)| 00:00:01 |
| 1 | DELETE | x_table | | | | |
|* 2 | INDEX UNIQUE SCAN| PK_x_table| 1 | 17 | 2 (0)| 00:00:01 |
--------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------------------
---------------------------------------------------

2 - access("x_column"=60)

14 rows selected.


Regards,
Joy
Martin Vajsar
Sheriff

Joined: Aug 22, 2010
Posts: 3610
    
  60

Oracle's EXPLAIN PLAN can be used to display the query plan - steps that the database will use to execute the statement. Even though your statement is not a complicated one, you can see that the database will use an index (PK_x_table) when accessing the row you want to delete.

EXPLAIN PLAN is usually used when 'tuning' the SQL statements - making changes that would result into the statement being executed more efficiently. This is actually a vast and somewhat complicated area of expertise, but if you want to get better understanding of it, you might start with this documentation, for example.


Jeanne Boyarsky
internet detective
Marshal

Joined: May 26, 2003
Posts: 30392
    
150

As Martin noted, you can see that your query uses and index - which is good. If it were using a table scan, the explain plan would be telling you that you should look into making your query more efficient.


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