Oracle General

Following on from my previous few posts on “data skew”, I’m now going to look at it from a slightly different perspective, where there is an inherent relationship between columns. The CBO has difficulties in recognising (by default) that some combinations of column values are far more common than other combinations, resulting in incorrect cardinality […]

  I’m going to expand just a tad on my previous posts on data skew and run a simple query that returns a few rows based on a column predicate AND another query on the same column that returns many rows. The following table has a CODE column as with previous posts with the data […]

In my previous post, I discussed an example with data skew, in which the Automatic Indexing process created a new index, but somehow the CBO when using the index estimated the correct cardinality estimate even though no histograms were explicitly calculated. In this post I’ll answer HOW this achieved by the CBO. Get some idea […]