SQL Tuning 基础概述02 - Explain plan的使用

SQL Tuning 基础概述02 - Explain plan的使用

1.explain plan的使用

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SQL> explain plan for delete from t_jingyu;   Explained.   SQL> select * from table(dbms_xplan.display);   PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------------------------------------------------------------------- Plan hash value: 1368587462   ----------------------------------------------------------------------- | Id  | Operation          | Name     | Rows  | Cost (%CPU)| Time     | ----------------------------------------------------------------------- |   0 | DELETE STATEMENT   |          |  1864K|   978   (2)| 00:00:12 | |   1 |  DELETE            | T_JINGYU |       |            |          | |   2 |   TABLE ACCESS FULL| T_JINGYU |  1864K|   978   (2)| 00:00:12 | -----------------------------------------------------------------------   Note -----    - dynamic sampling used for this statement (level=2)   13 rows selected

 2.explain plan 只是显示执行计划，并不会真正执行delete语句·

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SQL> select count(*) from t_jingyu;     COUNT(*) ----------    2097152