BE storage Engine has some bug in Date comparison, and hence if we push down predicates like Date'x' < Date 'y', we get error results. This pr just convert expr like ’Date'x' < Date 'y',‘ to DateTime'x' < DateTime 'y' TODO: do storage engine support date slot compare with datetime? if it support, we could avoid add cast on the slot and then, this expression could push down to storage engine.