如何在 Oracle 12c 中调整 all_constraints 上的查询？

Question

如何调整以下查询，因为它大约需要 8 秒：

select constraint_name,table_name
                from  all_constraints 
         where  r_constraint_name in
                               (select  constraint_name
                                  from  all_constraints
                                where table_name='SUPPLIER');

SUPPLIER 是一个示例表名。

Answer 1

在查询字典视图时，规则提示通常会有所帮助。

select /*+ RULE */ constraint_name,table_name
                from  all_constraints 
         where  r_constraint_name in
                               (select  constraint_name
                                  from  all_constraints
                                where table_name='SUPPLIER');

但是您的查询并不准确。对象也有所有者。

select /*+ RULE */ owner, constraint_name,table_name
                from  all_constraints 
         where  (r_owner, r_constraint_name) in
                               (select  owner,constraint_name
                                  from  all_constraints
                                where table_name='SUPPLIER'
                                      and owner='SOMEONE');

但是这个查询可以被表述为一个连接。

select /*+ RULE +*/ ref.owner, ref.constraint_name,ref.table_name
  from  all_constraints ref, all_constraints cons
  where ref.r_constraint_name=cons.constraint_name
    and ref.r_owner=cons.owner
    and cons.owner='&OWNER'
    and cons.table_name='&TABLE';

如果您更喜欢现代 JOIN 语法

select /*+ RULE */ ref.owner, ref.constraint_name,ref.table_name
  from  all_constraints ref JOIN all_constraints cons 
    on (ref.r_owner=cons.owner and ref.r_constraint_name=cons.constraint_name)
  where 
  cons.owner='&OWNER'
  and cons.table_name='&TABLE';

这是一些计时结果，在 12c 数据库 (12.1.0.2.0) 上有和没有规则提示

SQL> alter system flush shared_pool;     

System altered.

Elapsed: 00:00:00.44
SQL> select ref.owner, ref.constraint_name,ref.table_name
  2    from  all_constraints ref, all_constraints cons
  3    where ref.r_constraint_name=cons.constraint_name
  4    and ref.r_owner=cons.owner
  5    and cons.owner='OWNER'
  6    and cons.table_name='TABLE';

no rows selected

Elapsed: 00:00:03.95
SQL> select ref.owner, ref.constraint_name,ref.table_name
  2    from  all_constraints ref, all_constraints cons
  3    where ref.r_constraint_name=cons.constraint_name
  4    and ref.r_owner=cons.owner
  5    and cons.owner='OWNER'
  6    and cons.table_name='TABLE';

no rows selected

Elapsed: 00:00:00.00
SQL> alter system flush shared_pool;   

System altered.

Elapsed: 00:00:00.02
SQL> select ref.owner, ref.constraint_name,ref.table_name
  2    from  all_constraints ref, all_constraints cons
  3    where ref.r_constraint_name=cons.constraint_name
  4    and ref.r_owner=cons.owner
  5    and cons.owner='OWNER'
  6    and cons.table_name='TABLE';

no rows selected

Elapsed: 00:00:03.94
SQL> alter system flush shared_pool;

System altered.

Elapsed: 00:00:00.01
SQL> select /*+ RULE */ ref.owner, ref.constraint_name,ref.table_name
  2    from  all_constraints ref, all_constraints cons
  3    where ref.r_constraint_name=cons.constraint_name
  4    and ref.r_owner=cons.owner
  5    and cons.owner='OWNER'
  6    and cons.table_name='TABLE';

no rows selected

Elapsed: 00:00:00.27
SQL> select /*+ RULE */ ref.owner, ref.constraint_name,ref.table_name
  2    from  all_constraints ref, all_constraints cons
  3    where ref.r_constraint_name=cons.constraint_name
  4    and ref.r_owner=cons.owner
  5    and cons.owner='OWNER'
  6    and cons.table_name='TABLE';

no rows selected

Elapsed: 00:00:00.16

我还使用以下方法收集了有关 SYS 对象的统计信息

SQL> exec dbms_stats.gather_schema_stats('SYS',options=>'GATHER', -
> estimate_percent => DBMS_STATS.AUTO_SAMPLE_SIZE, -
> method_opt => 'FOR ALL COLUMNS SIZE AUTO', cascade => TRUE);

PL/SQL procedure successfully completed.

Elapsed: 00:03:41.58

但这没有帮助。

在 11g 系统 (11.2.0.4.0) 上，没有提示的查询性能要好得多，但即使有提示也会加速查询

SQL> alter system flush shared_pool;

System altered.

Elapsed: 00:00:00.01
SQL> select  ref.owner, ref.constraint_name,ref.table_name
  2    from  all_constraints ref, all_constraints cons
  3    where ref.r_constraint_name=cons.constraint_name
  4    and ref.r_owner=cons.owner
  5    and cons.owner='OWNER'
  6    and cons.table_name='TABLE';

no rows selected

Elapsed: 00:00:00.65
SQL> alter system flush shared_pool;

System altered.

Elapsed: 00:00:00.01
SQL> select  ref.owner, ref.constraint_name,ref.table_name
  2    from  all_constraints ref, all_constraints cons
  3    where ref.r_constraint_name=cons.constraint_name
  4    and ref.r_owner=cons.owner
  5    and cons.owner='OWNER'
  6    and cons.table_name='TABLE';

no rows selected

Elapsed: 00:00:00.66
SQL> alter system flush shared_pool;

System altered.

Elapsed: 00:00:00.01
SQL> select /*+ RULE */ ref.owner, ref.constraint_name,ref.table_name
  2    from  all_constraints ref, all_constraints cons
  3    where ref.r_constraint_name=cons.constraint_name
  4    and ref.r_owner=cons.owner
  5    and cons.owner='OWNER'
  6    and cons.table_name='TABLE';

no rows selected

Elapsed: 00:00:00.18
SQL>