oracle执行计划阅读

oracle执行计划阅读
英文回答：
Understanding Oracle Execution Plans.
An Oracle execution plan is a detailed representation
of the steps that the Oracle database will take to execute
a SQL statement. It provides valuable information about how the database will retrieve and process data, and can be
used to identify potential performance bottlenecks and optimize queries.
The execution plan is generated by the Oracle optimizer, which takes into account the structure of the tables involved, the indexes available, and the statistics
collected by the database. The optimizer chooses the plan that is expected to execute the statement with the best possible performance.
An execution plan can be viewed using the EXPLAIN PLAN
statement. This statement will display the plan in a graphical or textual format, showing the operations that will be performed and the estimated cost of each operation.
The following is an example of an execution plan for a simple SELECT statement:
EXPLAIN PLAN FOR.
SELECT.
FROM customers.
WHERE customer_id = 10;
Plan:
--------------------------------------------------------------------------------------------------------------------。

| Id | Operation | Name | Rows | Bytes | Cost
(%CPU)| Time |。

-------------------------------------------------------
-----------------------------------------------------------
--。

| 0 | SELECT STATEMENT | | 4656 | 215552| 2 (0%)| 00:00:01 |。

| 1 | TABLE ACCESS FULL| CUSTOMERS | 4656 | 215552| 2 (0%)| 00:00:01 |。

-------------------------------------------------------
-----------------------------------------------------------
--。

This plan shows that the database will perform a full table scan on the CUSTOMERS table to find the customer with the customer_id of 10. The estimated cost of the plan is 2, and the estimated execution time is 1 second.
Execution plans can be used to identify potential
performance bottlenecks. For example, if the plan shows that a table scan is being used to retrieve data, this could indicate that an index could be created to improve performance.
Execution plans can also be used to optimize queries. For example, if the plan shows that a subquery is being used to retrieve data, this could indicate that the subquery could be rewritten as a join to improve performance.
中文回答：
Oracle执行计划解读。

Oracle执行计划是对Oracle数据库执行SQL语句所采取的步骤的详细描述。

它提供了有关数据库如何检索和处理数据的重要信息，并且可以用来识别潜在的性能瓶颈和优化查询。

执行计划由Oracle优化器生成，它会考虑相关表的结构、可用的索引和数据库收集的统计信息。

优化器选择预计可以以最佳性能执行语句的计划。

可以使用EXPLAIN PLAN语句查看执行计划。

此语句将以图形或文本格式显示计划，显示要执行的操作和每个操作的估计成本。

以下是一个简单SELECT语句的执行计划示例：
EXPLAIN PLAN FOR.
SELECT.
FROM customers.
WHERE customer_id = 10;
计划：
--------------------------------------------------------------------------------------------------------------------。

| Id | 操作 | 名称 | 行数 | 字节数 | 成本
(%CPU)| 时间 |。

-------------------------------------------------------
-----------------------------------------------------------
--。

| 0 | SELECT STATEMENT | | 4656 | 215552| 2 (0%)| 00:00:01 |。

| 1 | TABLE ACCESS FULL| CUSTOMERS | 4656 | 215552| 2 (0%)| 00:00:01 |。

-------------------------------------------------------
-----------------------------------------------------------
--。

此计划显示数据库将在CUSTOMERS表上执行一次全表扫描，以
查找customer_id为10的客户。

该计划的估计成本为2，估计执行
时间为1秒。

执行计划可用于识别潜在的性能瓶颈。

例如，如果该计划显示
正在使用表扫描来检索数据，则表明可以创建索引来提高性能。

执行计划也可用于优化查询。

例如，如果该计划显示正在使用子查询来检索数据，则表明可以将子查询重写为连接以提高性能。