Understand Oracle执行计划
程序员文章站
2022-06-17 17:38:50
...
一、什么是执行计划 An explain plan is a representation of the access path that is taken when a query is executed within
一、什么是执行计划
An explain plan is a representation of the access path that is taken when a query is executed within Oracle.
二、如何访问数据
三、执行计划层次关系
1.一个简单的例子:
SQL> select /*+parallel (e 4)*/ * from emp e;
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=1 Card=82 Bytes=7134)
1 PARALLEL_TO_SERIAL SELECT /*+ NO_EXPAND ROWID(A1) */ A1."EMPNO"
,A1."ENAME",A1."JOB",A1."MGR",A1."HI