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Column Groups

12.2.0.1 And Later Support (Limited) Extended Stats On Virtual columns / Column Groups of Expressions

I do have a demo as part of my optimizer related workshops that shows the restriction / limitation of DBMS_STATS not supporting extended statistics on virtual columns / group of expressions, so for example the combination of both expressions and column groups, like ((TRUNC(COL1)), (TRUNC(COL2))).

Surprisingly, when following a certain sequence of operation, this starts working (to some degree) from 12.2.0.1 on.

Column Groups - Edge Cases

Oracle 11g added Extended Statistics support for column groups in order to detect correlated columns for filter predicates using an equal comparison.

Note that Oracle 11g also added the ability to use the number of distinct keys of a composite index as an upper limit for the cardinality estimates for matching column predicates, which means that the optimizer is now capable of detecting correlated columns without the explicit addition of Extended Statistics / Column Groups.