Shulou(Shulou.com)06/01 Report--

I. description

In the process of viewing the execution plan test, it was encountered that the execution plan could not be viewed using dbms_xplan.display. It was found that the execution plan could be displayed normally after the set autot on was opened during the test and closed (set autot off).

II. Operation process

SQL > SQL > explain plan for select count (*) from tt;Explained.Elapsed: 00:00:00.00SQL > set lines 200 pages 2000SQL > select * from table (dbms_xplan.display ()) 9 rows selected.Elapsed: 00:00:00.02Execution Plan---Plan hash value: 2137789089 Murray- -| Id | Operation | Name | Rows | Bytes | Cost (% CPU) | Time |-- -| 0 | SELECT STATEMENT | | 8168 | 16336 | 29 (0) | 00:00:01 | | 1 | COLLECTION ITERATOR PICKLER FETCH | DISPLAY | 8168 | 16336 | 29 (0) | 00:00:01 | -Statistics-- -- 14 recursive calls 12 db block gets 55 consistent gets 0 physical reads 0 redo size 1124 bytes sent via SQL*Net to client 519 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 1 sorts (memory) 0 Execution plan cannot be displayed on sorts (disk) 9 rows processed## It's strange! # # close autot and check the execution plan again! SQL > set autot offSQL > select * from table (dbms_xplan.display ()) PLAN_TABLE_OUTPUT- -Plan hash value: 3133740314 muri- -| Id | Operation | Name | Rows | Cost (% CPU) | Time |- -| 0 | SELECT STATEMENT | | 1 | 21556 (1) | 00:04:19 | | 1 | SORT AGGREGATE | | 1 | | 2 | TABLE ACCESS FULL | TT | 2762K | 21556 (1) | 00:04:19 |- -- 9 rows selected.Elapsed: 00.02 rows selected.Elapsed # explain the execution plan The first is to do a full table scan, which is easy to understand, and sort aggregage is because of the count (*) aggregation. SQL >

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