SQL是结构化查询语⾔,是⼀种⽤来操作RDBMS(关系型数据库管理系统)的数据库语⾔,当前关系型数据库都⽀持使⽤SQL语⾔进⾏操作,也就是说可以通过SQL操作oracle,sqlserver,mysql等关系型数据库。 SQL语句主要分为 DDL语句:数据定义语⾔,这些语句定义了不同的数据段、数据库、表、列、索引等数据库对象...
在RDBMS中,无论那种数据库,都提供了SQL剖析工具,用来解决SQL效率低下的问题。在MongoDB中,也有相应的策略来实现剖析。MongoDB提供了db.collection.explain()方法, cursor.explain()方法,和explain命令去返回查询计划信息和查询计划的执行统计信息。这为我们诊断查询提供了极大的便利,本文主要描述db.collection.explain()...
Query 和Current 的总和为所访问的逻辑缓冲区的总数 执行下面命令:tkprof D:\ORACLE\PRODUCT\10.2.0\DB_1\RDBMS\TRACE/wgods_ora_3940.trc h:\out.txtoutputfile explain=etl/etl 执行上面命令后,可以查看生成的文本文件 复制代码 代码如下: TKPROF: Release 10.2.0.1.0 - Production on 星期三 5月 23 16:...
For example, run the commands inExample 9-2from a SQL*Plus session to create thePLAN_TABLEin theHRschema. Example 9-2 Creating a PLAN_TABLE CONNECT HR/your_password@$ORACLE_HOME/RDBMS/ADMIN/UTLXPLAN.SQLTable created. Oracle Corporation recommends that you drop and rebuild thePLAN_TABLEtable ...
如果要分析某条SQL的性能问题,通常我们要先看SQL的执行计划,看看SQL的每一步执行是否存在问题。如果一条SQL平时执行的好好的,却有一天突然性能很差,如果排除了系统资源和阻塞的原因,那么基本可以断定是执行计划出了问题。 看懂执行计划也就成了SQL优化的先决条件。这里的SQL优化指的是SQL性能问题的定位,定位后就可以...
I created a user MNASH and created a PLAN_TABLE in MNASH’s schema using $ORACLE_HOME/rdbms/admin/utlxplan.sql. This was in addition to the PUBLIC synonym PLAN_TABLE for the SYS.PLAN_TABLE$ temporary table created by default. SQL> explain plan for ...
Why do we need an associative table for many-to-many relationships? The UNIQUE constraint differs from the PRIMARY KEY constraint in what way? What is the purpose of a database, and how does the database accomplish this purpose? What is a RDBMS ...
• Object Databases:These days OOP concepts have also been introduced indatabasesystems to develop a newDBMSnamed object databases. These databases store the data directly in the form of objects. However, these databases are not as popular as the traditional RDBMS. ...
(OS) and other software are managed by the cloud provider. A good example of this is the Azure Database platform where the operating system and RDBMS are installed and configured by Microsoft, allowing you to start building database applications quickly. IaaS solutions are th...
For example, start a SQL*Plus session, connect with SYSDBA privileges, and run the script as follows: @$ORACLE_HOME/rdbms/admin/catplan.sql Oracle recommends that you drop and rebuild your local PLAN_TABLE table after upgrading the version of the database because the columns might change. ...