% improvement in collect stats after collecting

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% improvement in collect stats after collecting

HI,

I am new to the TERADATA technology.

Can anyone give me idea about how to know the % improvement in CollectStats after collecting on tables or columns. ??

Generally we collect Stats on tables and there columns but I am not getting how it will improve the system performance and how to know the % improvement in system performance after collecting stats. 

Is there any predefined steps to know the changes in Improvement ??

Is it possible that, after collecting stats the system performance will reduce ?? If yes then in which scenario ?? I heard that, over collecting stats will sometimes reduce the system performance.

Regards,

Deepak Dhabade