ISSUE:
 ------ Materialization of derived
 tables has been delayed until it is actually required, because of this
 estimation of row count of derived tables can no longer be as exact as it
 used to be. In some cases where GROUP BY clause of Query is optimized away
 because all group expressions can be reduced to some constant, we can say
 query can produce at most one row. But we are not using this info to
 calculate estimated row count. This lead to inaccurate estimates and hence
 suboptimal plan.

Fix:
----
For cases where GROUP BY CLAUSE is optimized away
because all group expressions are constants set
estimated_rowcount of the query to 1.