今天,开发同事说他在测试库执行一条SQL的时候,报ORA-01722: invalid number错误,但是在生产库和灰度库执行同一条SQL却能够正常执行,SQL如下:
select ItemStatus from BUS_CONTRACT where SerialNo=2016033100000047;
问了一下开发同事基本信息,得知SerialNo的字段类型为varchar2类型,此时未加引号,肯定是进行了隐式转换,但是为什么在生产库和灰度库却能够执行成功呢?带着如此疑问,进行了以下慢慢的摸索……
最初猜测是不是其他数据行的SerialNo字段存在带有字符的数据呢,但是查看了一下BUS_CONTRACT表的表结构,发现BUS_CONTRACT表的主键就是SerialNo字段,此时的查询,应该是可以走主键索引而不会全表扫描的,即便是其他数据行有带字符的数据,也不会被扫描到才是,可为什么会报错呢?
后来通过搜索网络上的文章,得知oracle在隐式转换时,如果是VARCHAR2->NUMBER转换,则不会导致索引失效,而如果是NUMBER->VARCHAR2的转换,此时则会让索引失效,很明显本次查询是NUMBER->VARCHAR2的转换,此时即便是有索引,oracle也不会走索引扫描而只会走全表扫描,查看其执行计划,果然如此:
SQL> set autotrace traceonly
SQL>
SQL> select ItemStatus from BUS_CONTRACT where SerialNo=2016033100000047;
ERROR:
ORA-01722: invalid number
no rows selected
Execution Plan
----------------------------------------------------------
Plan hash value: 809618537
---------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 21 | 661 (1)| 00:00:08 |
|* 1 | TABLE ACCESS FULL| BUS_CONTRACT | 1 | 21 | 661 (1)| 00:00:08 |
---------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter(TO_NUMBER("SERIALNO")=2016033100000047)
Statistics
----------------------------------------------------------
0 recursive calls
1 db block gets
2341 consistent gets
2392 physical reads
0 redo size
529 bytes sent via SQL*Net to client
519 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
0 rows processed
SQL>
SQL>
然后,通知开发同事,让他通过如下SQL看一下SerialNo字段是不是存在脏数据:
select ItemStatus,SerialNo from BUSI_CONTRACT;
开发人员反馈,果然是有一条记录不是纯数字而带有一些字符,让其删除该数据之后,查询正常。
建议跟隐式转换有关的SQL,最好还是带上引号,如下是SQL语句select ItemStatus from BUSI_CONTRACT where SerialNo='2016033100000047';的执行计划:
SQL>
SQL> select ItemStatus from BUS_CONTRACT where SerialNo='2016033100000047';
Execution Plan
----------------------------------------------------------
Plan hash value: 338903438
----------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
----------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 21 | 2 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| BUS_CONTRACT | 1 | 21 | 2 (0)| 00:00:01 |
|* 2 | INDEX UNIQUE SCAN | PK_BUS_CONTRACT | 1 | | 1 (0)| 00:00:01 |
----------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("SERIALNO"='2016033100000047')
Statistics
----------------------------------------------------------
1 recursive calls
0 db block gets
4 consistent gets
0 physical reads
0 redo size
528 bytes sent via SQL*Net to client
519 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
性能明显优于不带引号的,因为此时没有经历隐式转换,SQL执行走索引扫描了。
结论:1.涉及到隐式转换到字段最好加上引号,否则不会走索引;
2.隐式转换如果是VARCHAR2->NUMBER转换,则不会导致索引失效,而如果是NUMBER->VARCHAR2的转换,此时则会让索引失效;
3.之所以NUMBER->VARCHAR2会让索引失效,应该是转换为where to_number(name) = 123。
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