SQL> select /*+ RULE */ 2 A,B,C,D 3 from test 4 where b=113 5 and c=114 6 and a= 112 7 /
A B C D
---------- ---------- ---------- ------------------------------
112 113 114 test
Execution Plan ---------------------------------------------------------- 0 SELECT STATEMENT Optimizer=HINT: RULE 1 0 TABLE ACCESS (BY INDEX ROWID) OF 'TEST' 2 1 INDEX (RANGE SCAN) OF 'TEST_COMPOSITE' (NON-UNIQUE)
Is there a problem in the way I have specified the hint. It still seems to be using the index.
Thanks in advance Novice No more Oracle certifiable DBA
From: "Mark Richard" <[EMAIL PROTECTED]>
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Subject: Re: concatenated index
Date: Mon, 07 Jul 2003 20:09:24 -0800
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The order of the where clause is not important. Including the leading (first) columns in the index is. If you remove the "a = ?" element from any of the queries then it may stop using the index. Oracle is smart enough to look at the entire where clause and work out what it can do to achieve the result quickest.
You may be thinking on the rule based optimisor where the ordering of where clauses is significant - for cost based optimisor the order is essentially irrelevant.
Regards, Mark.
"Novice DBA"
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Sent by: Subject: concatenated index
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08/07/2003 13:44 Please respond to ORACLE-L
Dear all, I have a basic doubt. I grew up (in Oracle) believing that for the concatenated indexes to be used by a query the ordering of the columns in the where clause was very important. But now I have doubts I have a table test and a composite index on it.
CREATE TABLE TEST ( A NUMBER, B NUMBER, C NUMBER, D VARCHAR2 (30) ) ;
CREATE INDEX TEST_COMPOSITE ON TEST(A, B, C) ;
I inserted some test data into it(376833 rows)
Then tried some queries with explain plan. There is only one row which matches this criteria.
SQL> explain plan for 2 select * from test 3 where a= 112 4 and b=113 5 and c=114;
Explained.
SQL> @plan
Plan Table --------------------------------------------------------------------------------
| Operation | Name | Rows | Bytes| Cost | Pstart| Pstop | --------------------------------------------------------------------------------
| SELECT STATEMENT | | 5K| 74K| 88 | |
| | TABLE ACCESS BY INDEX ROW|TEST | 5K| 74K| 88 | |
| | INDEX RANGE SCAN |TEST_COMP | 5K| | 39 | |
| --------------------------------------------------------------------------------
6 rows selected.
SQL> explain plan for 2 select * from test 3 where a= 112 4 and c=114 5 and b=113;
Explained.
SQL> @plan
Plan Table --------------------------------------------------------------------------------
| Operation | Name | Rows | Bytes| Cost | Pstart| Pstop | --------------------------------------------------------------------------------
| SELECT STATEMENT | | 5K| 74K| 88 | |
| | TABLE ACCESS BY INDEX ROW|TEST | 5K| 74K| 88 | |
| | INDEX RANGE SCAN |TEST_COMP | 5K| | 39 | |
| --------------------------------------------------------------------------------
6 rows selected.
SQL> explain plan for 2 select * from test 3 where b=113 4 and a= 112 5 and c=114;
Explained.
SQL> @plan
Plan Table --------------------------------------------------------------------------------
| Operation | Name | Rows | Bytes| Cost | Pstart| Pstop | --------------------------------------------------------------------------------
| SELECT STATEMENT | | 5K| 74K| 88 | |
| | TABLE ACCESS BY INDEX ROW|TEST | 5K| 74K| 88 | |
| | INDEX RANGE SCAN |TEST_COMP | 5K| | 39 | |
| --------------------------------------------------------------------------------
6 rows selected.
SQL> explain plan for 2 select * from test 3 where b=113 4 and c=114 5 and a= 112;
Explained.
SQL> @plan
Plan Table --------------------------------------------------------------------------------
| Operation | Name | Rows | Bytes| Cost | Pstart| Pstop | --------------------------------------------------------------------------------
| SELECT STATEMENT | | 5K| 74K| 88 | |
| | TABLE ACCESS BY INDEX ROW|TEST | 5K| 74K| 88 | |
| | INDEX RANGE SCAN |TEST_COMP | 5K| | 39 | |
| --------------------------------------------------------------------------------
6 rows selected.
SQL> explain plan for 2 select * from test 3 where b=113 4 and c=114;
Explained.
SQL> @plan
Plan Table --------------------------------------------------------------------------------
| Operation | Name | Rows | Bytes| Cost | Pstart| Pstop | --------------------------------------------------------------------------------
| SELECT STATEMENT | | 23K| 299K| 158 | |
| | TABLE ACCESS FULL |TEST | 23K| 299K| 158 | |
| --------------------------------------------------------------------------------
Now I am at loss. I know this is something very basic. But I am unable to understand why the index is being used even when the order of the columns in the where clause is changed.
Oracle version 8.1.7.2.
Please enlighten me
Thanks in advance
Novice No more Oracle Certifiable DBA
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