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oracle中Like与Instr的性能比较

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Release: 2016-06-07 15:44:29
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t表中将近有1100万数据,很多时候,我们要进行字符串匹配,在SQL语句中,我们通常使用like来达到我们搜索的目标。但经过实际测试发现,like的效率与instr函数差别相当大。下面是一些测试结果: SQL set timing on SQL select count(*) from t where instr(ti

t表中将近有1100万数据,很多时候,我们要进行字符串匹配,在SQL语句中,我们通常使用like来达到我们搜索的目标。但经过实际测试发现,like的效率与instr函数差别相当大。下面是一些测试结果:

SQL> set timing on
SQL> select count(*) from t where instr(title,’手册’)>0;

COUNT(*)
———-
65881

Elapsed: 00:00:11.04
SQL> select count(*) from t where title like ‘%手册%’;

COUNT(*)
———-
65881

Elapsed: 00:00:31.47
SQL> select count(*) from t where instr(title,’手册’)=0;

COUNT(*)
———-
11554580

Elapsed: 00:00:11.31
SQL> select count(*) from t where title not like ‘%手册%’;

COUNT(*)
———-
11554580

另外,我在另外一个2亿多的表,使用8个并行,使用like查询很久都不出来结果,但使用instr,4分钟即完成查找,性能是相当的好。这些小技巧用好,工作效率提高不少。通过上面的测试说明,ORACLE内建的一些函数,是经过相当程度的优化的。

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