http://zhidao.baidu.com/link?url=APKpO_ktmLa4QE0ZYlOqKyNdLul4rkDbV-LXBeDv40sHe0yDXS-LGc4A3ArNL2Ro-TTSb0SbSOM8Co1xhBf5PR9iX5eU6yV-fznLs_0OJhyalter system flush shared_pool ; alter system flush BUFFER_CACHE ; ...【阅读全文】
--SQL基础-->层次化查询(START BY ... CONNECT BY PRIOR)--====================================================== 层次化查询,即树型结构查询,是SQL中经常用到的功能之一,通常由根节点,父节点,子节点,叶节点组成,其语法如下: SELECT [LEVEL] ,column,expressi...【阅读全文】
在ITPUB上遇到一个很有意思的问题(http://www.itpub.net/thread-1796130-1-1.html),对于表T,有object_id,按照where object_id =:oid查询,如果传入的oid是NULL,则查询全部(希望走全表扫描),相当于FROM t WHERE 1=1,如果object_id传入非NULL值(希望走索引扫描),则执行查询FROM t WHERE object_id =:oid,这是常见的根据传入的值不同,执行不同条件查询的语句。【阅读全文】
eg:1. Find the execution plan and it will be imported into plan_tableSQL> explain plan for select e.EMPLOYEE_ID,e.FIRST_NAME,e.LAST_NAME, d.DEPARTMENT_NAME from employees e, departments d where e.DEPARTMENT_ID=d.DEPARTMENT_ID a...【阅读全文】