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

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SQL_ID4uuk2mdgh036f, child number 0

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select t1.* from t1,t2 where t1.id=t2.id and t1.id<3

Plan hash value: 1106359941

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| 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 |

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Predicate Information (identified by operation id):

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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(*)

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131072

A-Rows 真实返回的记录数

E-Rows Oracle预估的返回记录数