1.autotrace的設定

SQL> set autotrace Usage: SET AUTOT[RACE] {OFF | ON | TRACE[ONLY]} [EXP[LAIN]] [STAT[ISTICS]] set autot on --打開autotrace，之后執行的sql，會顯示sql執行結果、執行計劃、統計信息set autot on exp --會顯示sql執行結果、執行計劃set autot on stat --會顯示sql執行結果、統計信息set autot trace --只顯示執行計劃、統計信息set autot trace exp --只顯示執行計劃（可能不準,sql查詢并沒有真正執行）set autot trace stat --只顯示統計信息set autot off --關閉autotrace

2.實驗驗證 set autot trace exp 沒有真正執行查詢類sql：

SQL> set autot trace exp SQL> select * from t_jingyu; Elapsed: 00:00:00.04Execution Plan ---------------------------------------------------------- Plan hash value: 2809386205------------------------------------------------------------------------------ | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------ | 0 | SELECT STATEMENT | | 1864K| 69M| 981 (2)| 00:00:12 | | 1 | TABLE ACCESS FULL| T_JINGYU | 1864K| 69M| 981 (2)| 00:00:12 | ------------------------------------------------------------------------------Note ------ dynamic sampling used for this statement (level=2)SQL> set autot trace SQL> select * from t_jingyu;2097152 rows selected.Elapsed: 00:00:24.89Execution Plan ---------------------------------------------------------- Plan hash value: 2809386205------------------------------------------------------------------------------ | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ------------------------------------------------------------------------------ | 0 | SELECT STATEMENT | | 1864K| 69M| 981 (2)| 00:00:12 | | 1 | TABLE ACCESS FULL| T_JINGYU | 1864K| 69M| 981 (2)| 00:00:12 | ------------------------------------------------------------------------------Note ------ dynamic sampling used for this statement (level=2)Statistics ----------------------------------------------------------0 recursive calls0 db block gets143066 consistent gets3484 physical reads0 redo size51171186 bytes sent via SQL*Net to client1538429 bytes received via SQL*Net from client139812 SQL*Net roundtrips to/from client0 sorts (memory)0 sorts (disk)2097152 rows processedSQL> --試驗表明set autot trace exp不真正執行sql顯示的執行計劃，set autot trace 執行了sql顯示的執行計劃。

總結

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