Oracle 执行计划了的rows概念

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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_ID4uuk2mdgh036f, child number 0-------------------------------------select t1.* from t1,t2 where t1.id=t2.id and t1.id<3Plan 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(*)----------    131072A-Rows 真实返回的记录数 E-Rows Oracle预估的返回记录数
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