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SQL Optimizer for Oracle 10.0 - User Guide

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ALL PARTITION ALTER INDEX AND EQUAL ANTI JOIN BITMAP AND BITMAP COMPACTION BITMAP CONSTRUCTION BITMAP CONVERSION BITMAP INDEX BITMAP JOIN INDEX UPDATE BITMAP JOIN INDEX UPDATE STATEMENT BITMAP KEY ITERATION BITMAP MERGE BITMAP MINUS BITMAP OR BUFFER SORT CARTESIAN JOIN COLLECTION ITERATOR CONCATENATION CONNECT BY CONNECT BY PUMP COUNT COUNT STOPKEY CREATE AS SELECT CUBE SCAN DDL STATEMENT DELETE DOMAIN INDEX FAST FULL INDEX SCAN FILTER FIRST ROWS FIXED INDEX FIXED TABLE FOR UPDATE FULL INDEX SCAN FULL INDEX SCAN DESCENDING FULL INDEX SCAN (MIN/MAX) HASH GROUP BY HASH GROUP BY PIVOT HASH JOIN HASH JOIN BUFFERED HASH PARTITION HASH UNIQUE INDEX INDEX BUILD NON UNIQUE INDEX RANGE SCAN INDEX RANGE SCAN DESCENDING INDEX RANGE SCAN (MIN/MAX) INDEX SAMPLE FAST FULL SCAN INDEX SKIP SCAN INDEX SKIP SCAN DESCENDING INDEX UNIQUE SCAN INLIST ITERATOR INLIST PARTITION INSERT INTERSECTION INTO INVALID PARTITION ITERATOR PARTITION LOAD AS SELECT MAT_VIEW ACCESS MAT_VIEW REWRITE ACCESS MERGE JOIN MINUS MULTI-TABLE INSERT NESTED LOOPS OUTER JOIN PARTITION PARTITION HASH EMPTY PARTITION LIST PARTITION RANGE PROJECTION PX BLOCK ITERATOR PX COORDINATOR PX ITERATOR PX PARTITION PX PARTITION HASH ALL PX PARTITION LIST ALL PX PARTITION RANGE ALL PX RECEIVE PX SEND RANGE PARTITION RECURSIVE EXECUTION RECURSIVE WITH PUMP REFERENCE MODEL REMOTE SELECT SEMI JOIN SEQUENCE SINGLE PARTITION SINGLE RANGE PARTITION SORT SORT AGGREGATE SORT GROUP BY SORT GROUP BY CUBE SORT GROUP BY NOSORT SORT GROUP BY ROLLUP SORT JOIN SORT ORDER BY SORT UNIQUE SQL MODEL TABLE ACCESS TABLE ACCESS BY GLOBAL INDEX ROWID TABLE ACCESS BY INDEX ROWID TABLE ACCESS BY LOCAL INDEX ROWID TABLE ACCESS BY ROWID TABLE ACCESS BY USER ROWID TABLE ACCESS CLUSTER TABLE ACCESS FULL TABLE ACCESS HASH TABLE ACCESS SAMPLE TABLE QUEUE TEMP TABLE GENERATION TEMP TABLE TRANSFORMATION UNION UNION ALL UNION ALL (RECURSIVE WITH) UNPIVOT UPDATE VIEW VIEW PUSHED PREDICATE WINDOW
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REMOTE

Execution Plan image: image\Plan_Remote_Stmt.gif   

Row or Set operation.

REMOTE .PLAN_TABLE column of Other sends a SQL statement to be executed at a remote node via a database link. The syntax of the SQL statement sent to the remote node is shown in the

Example

Since REMOTE requires a remote database access, a database link is created for this example. The database link connects to the Hobbes account in the database that is identified via the 'test' service name in the local tnsnames.ora file.

create database link REMOTE1
connect to hobbes identified by tiger
using 'test';

In the example query, a local COMPANY is joined to a remote SALES via a NESTED LOOPS join.

Example

select COMPANY.Name
from COMPANY, SALES@REMOTE1
where COMPANY.Company_ID = SALES.Company_ID
and SALES.Period_ID = 3
and SALES.Sales_Total > 1000;

Execution Plan

NESTED LOOPS
REMOTE
TABLE ACCESS BY ROWID COMPANY
INDEX UNIQUE SCAN COMPANY_PK

For the step with the REMOTE operation, you can query PLAN_TABLE for the syntax of the query sent to the remote node:

select Other
from PLAN_TABLE
where Operation = 'REMOTE';

The value of the Other column for this example is:

SELECT "COMPANY_ID","PERIOD_ID","SALES_TOTAL"
FROM "SALES" SALES
WHERE "SALES_TOTAL">1000 AND "PERIOD_ID"=3

Interpreting the Execution Plan

The Execution Plan shows that the remote SALES table is used as the driving table for the NESTED LOOPS join (see the NESTED LOOPS operation for a brief discussion of driving tables). The text in the PLAN_TABLE. The Other column shows the query that is executed in the remote database. For each Company_ID value returned by the query of the remote SALES table, the COMPANY_PK index is checked to see if a matching Company_ID value exists in the COMPANY table. When a match exists, that row is returned to the user by using the NESTED LOOPS operation.

 

SELECT

Execution plan image: image\Plan_Select_Stmt.gif

The SELECT statement retrieves data from one or more tables, object tables, views, object views, or materialized views.

Note: When the result (or part of the result) of a SELECT statement is equivalent to an existing materialized view, Oracle may use the materialized view in place of one or more tables specified in the SELECT statement. This substitution is called query rewrite, and takes place only if cost optimization is enabled and the Oracle QUERY_REWRITE_ENABLED parameter is set to TRUE.

Prerequisites

To select data from a table or materialized view, the table or materialized view must be included in your own schema or you must have the SELECT privilege on the table or materialized view.

To select rows from the base tables of a view

  • You must have the SELECT privilege on the view.

  • The owner of the schema containing the view must have the SELECT privilege on the base tables.

The SELECT ANY TABLE system privilege also allows you to select data from any table or any materialized view or any view's base table.

 

Related Topics

 

SEMI JOIN

Execution Plan image: image\Plan_Connect_By_Semi.gif, image\Plan_Merge_Join_Semi.gif, image\Plan_Nested_Loops.gif or image\Plan_Hash_Join.gif

Join operation.

A SEMI JOIN is a join which returns rows from a table which have matching rows in a second table but which does not return multiple rows if there are multiple matches. This is usually expressed in Oracle using a WHERE EXISTS sub-query.

 

Related Topics

 

SEQUENCE

Execution Plan image: image\Plan_Sequence.gif  

Row operation.

SEQUENCE pseudo-columns. CurrVal and NextVal is used when accessing a database sequence via the

Example

Since the SEQUENCE operation requires a sequence to exist, a sequence named COMPANY_ID_SEQ is created.

create sequence COMPANY_ID_SEQ
start with 1 increment by 1;

In the example query, the next value is selected from the sequence by selecting the NextVal pseudo-column from DUAL.

select COMPANY_ID_SEQ.NextVal
from DUAL;

Execution Plan

SEQUENCE COMPANY_ID_SEQ
TABLE ACCESS FULL DUAL

Interpreting the Execution Plan

The Execution Plan shows that the DUAL table (comprising 1 row, and owned by SYS) is scanned. The COMPANY_ID_SEQ sequence is used to generate the value of the NextVal pseudo-column for the returned row, using the SEQUENCE operation.

 

Related Topics

 

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