SQL 执行计划案例1

http://www.bitscn.com/pdb/oracle/200809/151545.html

RESOLVE METHOD:

CHECK EXECUTE PLAN:

SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY);

1, CHECK IF THERE IS CARTESIAN .

2，CHECK TABLE STATISTICS.

3, IF USE PREDICT FILTER ON TABLE, THEN CHECK COLUMN STATISTICS .

4, UPDATE TABLE STATISTICS.

SQL> EXEC DBMS_STATS.DELETE_TABLE_STATS(USER, 'ORD_HIT_COMM')
　　PL/SQL procedure successfully completed.
　　SQL> EXEC DBMS_STATS.GATHER_TABLE_STATS(USER, 'ORD_HIT_COMM')
　　PL/SQL procedure successfully completed.

5, CHECK STATISTICS.

SELECT COLUMN_NAME, NUM_DISTINCT, NUM_NULLS, DENSITY, NUM_BUCKETS
　　 FROM USER_TAB_COLUMNS
　　 WHERE TABLE_NAME = 'ORD_HIT_COMM'
　　 AND COLUMN_NAME = 'ENABLE_FLAG';

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