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Message Posted: Mon, 15 Oct 2001 @ 15:23:12 GMT


     
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Subj:   Re: Stats always desirable (was Join question)
 
From:   Petr Horsky

I had dropped the statistics of the unevenly distributed column and the query completed in 28 secs (instead of one hour 35 minutes with the stats). There were stats collected on all columns that are in predicates of the query including the one row table. There were also stats collected on all PIs, ther are no other indexes.

My question is: does COLLECT STATISTICS provide the optimizer with any other info than the number of unique values? The manual says YES, but where is it stored and how can I retrieve it? HELP STATISTICS returns only the number of unique values.

Whatever the answer is, I find alarming, that adding stats when tuning one query may have disastrous impact on another query (probably hidden somewhere in daily transformation batches or even worth generated by ETL or reporting tools) - which was exactly this case.

If anybody is interested, I can mail you the query and details of the tables involved.

Petr Horsky



     
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