基础知识之游标共享----CURSOR_SHARING

SQL> show parameter cursor_sharingNAME                                 TYPE        VALUE------------------------------------ ----------- ------------------------------cursor_sharing                       string      EXACT--上述参数完全依赖开发人员自行绑定变量，或者同样的sql标准化编写SQL> alter system flush shared_pool;系统已更改。SQL> select sql_id,child_number,sql_text from v$sql where sql_text like 'selectcount(*) from%';未选定行SQL> select count(*) from test where object_id<10;  COUNT(*)----------        24SQL> select count(*) from test where object_id<100;  COUNT(*)----------       294SQL> select count(*) from test where object_id<1000;  COUNT(*)----------      2826SQL> select sql_id,child_number,sql_text from v$sql where sql_text like 'selectcount(*) from%';SQL_ID        CHILD_NUMBER SQL_TEXT------------- ------------ -----------------------------------------------------13u8w83yzd77c            0 select count(*) from test where object_id<1000dft4kr6s6yd8q            0 select count(*) from test where object_id<100355kdmgpm6upg            0 select count(*) from test where object_id<10SQL> show parameter cursor_sharingNAME                                 TYPE        VALUE------------------------------------ ----------- ------------------------------cursor_sharing                       string      EXACTSQL> alter session set cursor_sharing=FORCE;会话已更改。SQL> select count(*) from test where object_id<20;  COUNT(*)----------        54SQL> select count(*) from test where object_id<200;  COUNT(*)----------       573SQL> select count(*) from test where object_id<2000;  COUNT(*)----------      5793SQL> select sql_id,child_number,sql_text from v$sql where sql_text like 'selectcount(*) from%';SQL_ID        CHILD_NUMBER SQL_TEXT------------- ------------ -----------------------------------------------------crwtm662ycm4w            0 select count(*) from sys.job$ where next_date < :1 an13u8w83yzd77c            0 select count(*) from test where object_id<1000dft4kr6s6yd8q            0 select count(*) from test where object_id<1008uahcgc6uypzg            0 select count(*) from test where object_id<:"SYS_B_0"355kdmgpm6upg            0 select count(*) from test where object_id<10--此处强制绑定还有风险的，特别在谓词中的字段上编制了索引的时候