Oracle 执行计划了的rows概念

alter session set statistics_level=all;
select t1.* from t1,t2 where t1.id=t2.id and t1.id<3;
select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST')); 

SQL> select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST')); 

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SQL_ID	4uuk2mdgh036f, child number 0
-------------------------------------
select t1.* from t1,t2 where t1.id=t2.id and t1.id<3

Plan hash value: 1106359941

--------------------------------------------------------------------------------------------------
| Id  | Operation		     | Name    | Starts | E-Rows | A-Rows |   A-Time   | Buffers |
--------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT	     |	       |      1 |	 |    131K|00:00:00.34 |   37856 |
|   1 |  NESTED LOOPS		     |	       |      1 |      2 |    131K|00:00:00.34 |   37856 |
|   2 |   TABLE ACCESS BY INDEX ROWID| T1      |      1 |      3 |    131K|00:00:00.11 |   20376 |
|*  3 |    INDEX RANGE SCAN	     | T1_IDX1 |      1 |      3 |    131K|00:00:00.04 |    9392 |
|*  4 |   INDEX RANGE SCAN	     | T2_IDX1 |    131K|      1 |    131K|00:00:00.17 |   17480 |
--------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   3 - access("T1"."ID"<3)
   4 - access("T1"."ID"="T2"."ID")
       filter("T2"."ID"<3)

已选择23行。

SQL> select count(*) from t1 where t1.id<3;

  COUNT(*)
----------
    131072

A-Rows 真实返回的记录数

 E-Rows Oracle预估的返回记录数