explain oracke

回答: "Explain Oracle"是一个可以用来查看Oracle数据库中SQL语句的执行计划的功能。通过使用Explain，我们可以了解优化器是如何选择查询路径和使用索引的，从而帮助我们优化SQL语句。在PL/SQL中，可以在SQL窗口中输入要查询的SQL语句，然后按下F5键或在TOOLS菜单中选择Explain Plan菜单，即可查看该语句的执行计划。执行计划窗口会显示查询的路径和其他相关信息。在执行计划语句中，可以使用STATEMENT_ID参数来指定一个最优的STATEMENT_ID值，用于标识查询的执行计划。如果没有使用SET STATEMENT_ID语句，该值将被设为NULL。

相关问题

EXPLAIN oracle

Oracle是一个跨平台的关系型数据库管理系统，由Oracle公司开发。它提供了数据存储、管理、处理和分析的功能，广泛应用于企业级应用中。Oracle数据库可以在各种操作系统上运行，包括Windows、Linux和Unix等。Oracle数据库管理系统具有高度的可扩展性和安全性，并提供了丰富的功能和工具，如备份和恢复、性能优化、数据安全、数据复制等。

Oracle数据库系统基于SQL语言，支持事务处理和ACID特性，可以处理大量的数据和复杂的查询。它还提供了多种数据类型和索引类型，并支持分区和分布式数据库。Oracle还提供了多种工具和技术来管理和监控数据库，如Oracle Enterprise Manager和Oracle Real Application Clusters等。

总之，Oracle数据库是一个功能强大、可靠性高、可扩展性强的关系型数据库管理系统，被广泛应用于企业级应用和大型数据库系统中。

oracle explain

Oracle Explain Plan is a tool used for analyzing and understanding how Oracle will execute a SQL statement. It provides information on the operations that will be performed by Oracle to fetch the requested data, the order in which the operations will be executed, and the expected cost of each operation.

The Explain Plan is generated by the Oracle Optimizer, which analyzes the SQL statement and determines the most efficient way to execute it. The optimizer considers factors such as the available indexes, the size of the tables, and the complexity of the query.

The Explain Plan can be obtained using the EXPLAIN PLAN statement or by using tools such as SQL Developer or Toad. The output of the Explain Plan includes the execution plan, the estimated number of rows, and the cost of each operation.

The execution plan provides a visual representation of the operations that Oracle will perform to execute the SQL statement. The estimated number of rows indicates the number of rows that Oracle expects to retrieve for each operation. The cost of each operation is an estimate of the resources required to execute the operation, including disk I/O, CPU time, and memory usage.

The Explain Plan is a valuable tool for optimizing SQL statements and improving the performance of Oracle databases. By analyzing the plan, database administrators and developers can identify potential bottlenecks and make changes to the SQL statement or database schema to improve performance.