>A quick search led me to
>https://dba.stackexchange.com/questions/84747/statistics-are-multicolumn-histograms-possible
>which contains a pointer to
>https://blogs.msdn.microsoft.com/ianjo/2005/11/10/create-multi-column-statistics/
>
>then you can see the MS docs at
>https://docs.microsoft.com/en-us/sql/t-sql/statements/create-statistics-transact-sql
>https://docs.microsoft.com/en-us/sql/relational-databases/statistics/statistics
For Oracle:
https://blogs.oracle.com/optimizer/extended-statistics