对于in和existsnot in和not exists还是有很多的人有疑惑更有甚者禁用not in所有的地方都要用not exists它真的高效吗？通过下面的使用我们来证明
先制造一些数据
SQL> drop table test purge;
SQL> drop table test purge;
SQL> create table test as select * from dba_objects where rownum <=;
SQL> create table test as select * from dba_objects;
SQL> exec dbms_statsgather_table_stats（usertest）
SQL> exec dbms_statsgather_table_stats（usertest）
SQL> set autotrace traceonly
in和exists原理及性能实验
SQL> select * from test t where tobject_id in （select tobject_id from test t）
已选择行
执行计划
Plan hash value:
| Id | Operation | Name | Rows | Bytes | Cost （%CPU）| Time |
| | SELECT STATEMENT | | | | （）| :: |
|* | HASH JOIN SEMI | | | | （）| :: |
| | TABLE ACCESS FULL| TEST | | | （）| :: |
| | TABLE ACCESS FULL| TEST | | K| （）| :: |
Predicate Information （identified by operation id）
access（TOBJECT_ID=TOBJECT_ID）
统计信息
recursive calls
db block gets
consistent gets
physical reads
redo size
bytes sent via SQL*Net to client
bytes received via SQL*Net from client
SQL*Net roundtrips to/from client
sorts （memory）
sorts （disk）
rows processed
SQL> select * from test t
where exists （select from test t where tobject_id = tobject_id）
已选择行
执行计划
Plan hash value:
| Id | Operation | Name | Rows | Bytes | Cost （%CPU）| Time |
| | SELECT STATEMENT | | | | （）| :: |
|* | HASH JOIN SEMI | | | | （）| :: |
| | TABLE ACCESS FULL| TEST | | | （）| :: |
| | TABLE ACCESS FULL| TEST | | K| （）| :: |
Predicate Information （identified by operation id）
access（TOBJECT_ID=TOBJECT_ID）
统计信息
recursive calls
db block gets
consistent gets
physical reads
redo size
bytes sent via SQL*Net to client
bytes received via SQL*Net from client
SQL*Net roundtrips to/from client
sorts （memory）
sorts （disk）
rows processed
结论在oracle g中in 和 exists其实是一样的原理就是两张表做HASH JOIN SEMI也可以通过事件看到两条sql语句最终转换成同一条sql
not in和not exists原理及性能实验
not exists 比 not in效率高的例子
SQL> select count（*） from test where object_id not in（select object_id from test）
执行计划
Plan hash value:
| Id | Operation | Name | Rows | Bytes | Cost （%CPU）| Time |
| | SELECT STATEMENT | | | | （）| :: |
| | SORT AGGREGATE | | | | | |
|* | FILTER | | | | | |
| | TABLE ACCESS FULL| TEST | | | （）| :: |
|* | TABLE ACCESS FULL| TEST | | | （）| :: |
Predicate Information （identified by operation id）
filter（ NOT EXISTS （SELECT /*+ */ FROM TEST TEST WHERE
LNNVL（OBJECT_ID<>:B）））
filter（LNNVL（OBJECT_ID<>:B））
统计信息
recursive calls
db block gets
consistent gets
physical reads
redo size
bytes sent via SQL*Net to client
bytes received via SQL*Net from client
SQL*Net roundtrips to/from client
sorts （memory）
sorts （disk）
rows processed
SQL> select count（*） from test t where not exists
（select from test t where tobject_id=tobject_id）
执行计划
Plan hash value:
| Id | Operation | Name | Rows | Bytes | Cost （%CPU）| Time |
| | SELECT STATEMENT | | | | （）| :: |
| | SORT AGGREGATE | | | | | |
|* | HASH JOIN ANTI | | | | （）| :: |
| | TABLE ACCESS FULL| TEST | | | （）| :: |
| | TABLE ACCESS FULL| TEST | | K| （）| :: |
Predicate Information （identified by operation id）
access（TOBJECT_ID=TOBJECT_ID）
统计信息
recursive calls
db block gets
consistent gets
physical reads
redo size
bytes sent via SQL*Net to client
bytes received via SQL*Net from client
SQL*Net roundtrips to/from client
sorts （memory）
sorts （disk）
rows processed
not in比not exists 效率高的例子
SQL> Set autotrace off
SQL> drop table test purge;
表已删除
SQL> drop table test purge;
表已删除
SQL> create table test as select * from dba_objects where rownum <=;
表已创建
SQL> create table test as select * from dba_objects;
表已创建
SQL> Insert into test select * from dba_objects;
已创建行
SQL> Insert into test select * from test;
已创建行
SQL> Insert into test select * from test;
已创建行
SQL> Commit;
提交完成
SQL> exec dbms_statsgather_table_stats（usertest）
PL/SQL 过程已成功完成
SQL> exec dbms_statsgather_table_stats（usertest）
PL/SQL 过程已成功完成
SQL> Set autotrace traceonly
SQL> select count（*） from test where object_id not in（select object_id from test）
执行计划
Plan hash value:
| Id | Operation | Name | Rows | Bytes | Cost （%CPU）| Time |
| | SELECT STATEMENT | | | | （）| :: |
| | SORT AGGREGATE | | | | | |
|* | FILTER | | | | | |
| | TABLE ACCESS FULL| TEST | | | （）| :: |
|* | TABLE ACCESS FULL| TEST | | | （）| :: |
Predicate Information （identified by operation id）
filter（ NOT EXISTS （SELECT /*+ */ FROM TEST TEST WHERE
LNNVL（OBJECT_ID<>:B）））
filter（LNNVL（OBJECT_ID<>:B））
统计信息
recursive calls
db block gets
consistent gets
physical reads
redo size
bytes sent via SQL*Net to client
bytes received via SQL*Net from client
SQL*Net roundtrips to/from client
sorts （memory）
sorts （disk）
rows processed
SQL> select count（*） from test t where not exists
（select from test t where tobject_id=tobject_id）
执行计划
Plan hash value:
| Id | Operation | Name | Rows | Bytes | Cost （%CPU）| Time |
| | SELECT STATEMENT | | | | （）| :: |
| | SORT AGGREGATE | | | | | |
|* | HASH JOIN ANTI | | | | （）| :: |
| | TABLE ACCESS FULL| TEST | | | （）| :: |
| | TABLE ACCESS FULL| TEST | K| K| （）| :: |
Predicate Information （identified by operation id）
access（TOBJECT_ID=TOBJECT_ID）
统计信息
recursive calls
db block gets
consistent gets
physical reads
redo size
bytes sent via SQL*Net to client
bytes received via SQL*Net from client
SQL*Net roundtrips to/from client
sorts （memory）
sorts （disk）
rows processed
结论not in 和not exists原理是nestedloops 与HASH JOIN的区别not in中的filter算法类似于nestedloops如果比较两者的性能就是比较nestedloops 与HASH JOIN的性能差异在本例子中
not in 性能 大于not exists test的数据量条test数量多万条
not exists 性能 大于not in test的数据量条test数量条
