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I can response the next query Oracle received lots of fudge elements, plus the concatentated index cardinality regulations aren well documented. In addition to, it an element that cancels alone out.

The AB be part of cardinality relies within the relative cardinality of the (one row) multiplied with the absolute cardinality of B (4897354) multiplied through the be a part of selectivity which can be one / absolute cardinality of the.

Look at it this fashion. Your tables map 12046 rows inside of a to 4897354 rows in B. As a result for each row in the, there are actually, on typical, 406 rows in B.

For a desk of 5M rows, a cardinality estimate of 406 isn't considerably diverse to 7366.

Thanks Jeffrey. You will be not surprisingly suitable in the cardinality estimate difference on this instance is not really considerable. Having said that, this is often merely a simplified circumstance I well prepared for this problem I have other cases of queries against exact tables where the primary difference is much even larger and presumably much more considerable also.

I am nevertheless not able to come up with the method Oracle takes advantage of to arrive at cardinality of 406. Num_distinct for columns a and b are 116 and 650, respectively. cartier tank solo replica Tom Jul 1 ten at 12 replica Breitling chronospace watches :39As spelled out there, simply because you have histograms, the filterfactor calculation for these columns would not use quantity of distinct values (NDV) but density, which is derived with the histogram in a roundabout way.

Generally, the situation in cases such as this is always that Oracle would not assemble data on pairs of columns, and assumes that their combined filter issue will probably be the product in their particular person factors. This will likely produce very low estimates if there is any correlation concerning values on the two columns.

If this is often producing a serious overall performance issue, I suppose you may build a functionbased index over a perform of all those columns, and use that to try and do the lookup. Then Oracle would assemble statistics on that index and possibly deliver better estimates.