Change default for USTAT_USE_IS_WHEN_NO_STATS This cqd was originally set to OFF by default, causing internal sort not to be used in cases where there are no existing histograms. Internal sort is known to underperform when there are a small number of unique values for a column, and without prior histograms, the unique entry count is unknown.
However, experience with POCs has shown that using internal sort in these situations (unique count unknown) is in general significantly faster than not using it, so the default setting has been changed to ON.
Running developer regressions with this setting exposed a bug that occurs when internal sort is used on an empty table that previously did contain rows. This change includes a known diffs file for the failing test until the bug (LP 1393930) can be fixed.