在oralce中给自建函数创建索引，结果不成功。
source:Create Index IDX_T_SP_TWOTYPESTAT_0_f On T_SP_TWOTYPESTAT_0(f_dateadd(yearmonth,12,2));
err:the function is not deterministic.
我们看一下这是为什么?
随便一个测试可以再现这个问题,我门创建一个函数(本范例函数用于进行16进制向10进制转换):
此时创建索引,获得如下错误信息:
如果需要创建基于自定义函数的索引,那么我们需要指定deterministic参数:
此时创建索引即可:
Oracle这样解释这个参数:
The hint DETERMINISTIC helps the optimizer avoid redundant function calls. If a stored function was called previously with the same arguments, the optimizer can elect to use the previous result. The function result should not depend on the state of session variables or schema objects. Otherwise, results might vary across calls. Only DETERMINISTIC functions can be called from a function-based index or a materialized view that has query-rewrite enabled.
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