[20180926]神奇的规避ORA-01795方法.txt

[20180926]神奇的规避ORA-01795方法.txt

--//大家知道in里面的值限制1000个值,如果超出报ORA-01795错误.

D:\> ooerr 01795
01795, 00000, "maximum number of expressions in a list is 1000"

D:\> oerr ora 01795
01795, 00000, "maximum number of expressions in a list is 1000"
// *Cause:    Number of expressions in the query exceeded than 1000.
//            Note that unused column/expressions are also counted
//            Maximum number of expressions that are allowed are 1000.
// *Action:   Reduce the number of expressions in the list and resubmit.

--//别人的awr报表我仔细查看,发现对方规避ora-01795的方法,使用集合的概念,仔细一想难道集合就没有1000个的限制吗?
--//我仔细看对方程序是写死的,2000个集合,明显这样是没有问题的.
--//有时候还是给佩服开发的想象力,我还是做一些例子说明问题.

1.环境:
SCOTT@test01p> @ ver1

PORT_STRING                    VERSION        BANNER                                                                               CON_ID
------------------------------ -------------- -------------------------------------------------------------------------------- ----------
IBMPC/WIN_NT64-9.1.0           12.1.0.1.0     Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 - 64bit Production              0

SCOTT@test01p> create table t as select * from all_objects;
Table created.

SCOTT@test01p> create unique index i_t_object_id on t(object_id);
Index created.

--//分析表略.

2.测试1:
variable b1 number;
variable b2 number;
exec :b1 :=42;
exec :b2 :=47;

SCOTT@test01p> select * from t where (1,object_id) in ((1,:b1),(1,:b2));
OWNER OBJECT_NAME SUBOBJECT_NAME OBJECT_ID DATA_OBJECT_ID OBJECT_TYPE          CREATED             LAST_DDL_TIME       TIMESTAMP
----- ----------- -------------- --------- -------------- -------------------- ------------------- ------------------- -------------------
SYS   I_ICOL1                           42             42 INDEX                2013-06-28 09:03:29 2013-06-28 09:03:29 2013-06-28:09:03:29
SYS   I_USER2                           47             47 INDEX                2013-06-28 09:03:29 2013-06-28 09:03:29 2013-06-28:09:03:29

--//OK没有问题,里面仅仅包含2个集合,如果更多呢?

3.测试2:
select 'variable b'||to_char(level)||' number;' txt from dual connect by level<=1001
union all
select 'exec :b'||to_char(level)||' :='|| to_char(level) txt from dual connect by level<=1001
union all
select 'select * from t where (1,object_id) in (' txt from dual
union all
select '(1,:b'||to_char(level)||'),' txt from dual connect by level<=1000
union all
select '(1,:b'||to_char(1001)||'));' txt from dual ;

--//将输出保存1个脚本,适当编辑执行.ok,没有任何问题.执行计划如下:
Plan hash value: 3525592940

----------------------------------------------------------------------------------------------------------------------------------------
| Id  | Operation                    | Name          | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time   | A-Rows |   A-Time   | Buffers |
----------------------------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT             |               |      1 |        |       |   196 (100)|          |    891 |00:00:00.01 |      40 |
|   1 |  INLIST ITERATOR             |               |      1 |        |       |            |          |    891 |00:00:00.01 |      40 |
|   2 |   TABLE ACCESS BY INDEX ROWID| T             |   1001 |   1001 |   112K|   196   (0)| 00:00:01 |    891 |00:00:00.01 |      40 |
|*  3 |    INDEX UNIQUE SCAN         | I_T_OBJECT_ID |   1001 |   1001 |       |   178   (0)| 00:00:01 |    891 |00:00:00.01 |      22 |
----------------------------------------------------------------------------------------------------------------------------------------

--//1001个集合没有任何问题.
--//修改b200-b999变量等于0,测试看看:
Plan hash value: 3525592940

----------------------------------------------------------------------------------------------------------------------------------------
| Id  | Operation                    | Name          | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time   | A-Rows |   A-Time   | Buffers |
----------------------------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT             |               |      1 |        |       |   196 (100)|          |    193 |00:00:00.01 |      16 |
|   1 |  INLIST ITERATOR             |               |      1 |        |       |            |          |    193 |00:00:00.01 |      16 |
|   2 |   TABLE ACCESS BY INDEX ROWID| T             |    203 |   1001 |   112K|   196   (0)| 00:00:01 |    193 |00:00:00.01 |      16 |
|*  3 |    INDEX UNIQUE SCAN         | I_T_OBJECT_ID |    203 |   1001 |       |   178   (0)| 00:00:01 |    193 |00:00:00.01 |      12 |
----------------------------------------------------------------------------------------------------------------------------------------

--//可以发现starts=203,重复值不会扫描的.

4.我的估计:
--//对方2000个集合写死的,我估计可能是一个数组,初始赋值0(或者查询不到的值),然后赋值.
--//通过这样的方式实现绑定变量.
--//我个人还是趋向这样的方式使用临时表更加合理简单一些.