how to force oracle 12c to create histograms
A friend of mine told me today, that using the following command

begin
  DBMS_STATS.GATHER_TABLE_STATS (
    ownname =&gt; USER,
    tabname =&gt; 'H_LINEITEM',
    estimate_percent =&gt; 100,
    method_opt=&gt;'FOR ALL COLUMNS SIZE AUTO FOR COLUMNS SIZE 254 SYS_STU3ZM$X#P01D3JFWNOWKQ7DD$'
  );
end;
/


where SYS_STU3ZM$X#P01D3JFWNOWKQ7DD$ is the automatically generated name of the column group,

one can manually create a histogram for a given column / column group.

A description can be found here.