外键没有索引对性能的影响

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2、在从表的外键没有索引的时候，update主表上的一个数据delete主表上的一个数据是一样的要求。

SQL> update tmp_p set pk=100000 where pk=100001;

已更新 1 行。

执行计划

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Plan hash value: 3169732106

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--------------------------------------------------------------------------------

| 0 | UPDATE STATEMENT | | 1 | 5 | 1 (0)| 00:00:0

|* 2 | INDEX UNIQUE SCAN| SYS_C0034921 | 1 | 5 | 1 (0)| 00:00:0

--------------------------------------------------------------------------------

Predicate Information (identified by operation id):

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2 - access("PK"=100001)

统计信息

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7 recursive calls

9 db block gets

5654 consistent gets

0 physical reads

840 redo size

395 bytes sent via SQL*Net to client

330 bytes received via SQL*Net from client

4 SQL*Net roundtrips to/from client

1 sorts (memory)

0 sorts (disk)

1 rows processed

SQL>

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