protected override Expression VisitProjection(ProjectionExpression proj)
{
proj = (ProjectionExpression)base.VisitProjection(proj);
if (proj.Source.From is SelectExpression)
{
List <SelectExpression> redundant = RedundantSubqueryGatherer.Gather(proj.Source, Logger);
if (redundant != null)
{
proj = SubqueryRemover.Remove(proj, redundant, Logger);
}
}
return(proj);
}
protected override Expression VisitSelect(SelectExpression select)
{
select = (SelectExpression)base.VisitSelect(select);
// first remove all purely redundant subqueries
List <SelectExpression> redundant = RedundantSubqueryGatherer.Gather(select.From, Logger);
if (redundant != null)
{
select = SubqueryRemover.Remove(select, redundant, Logger);
}
// next attempt to merge subqueries that would have been removed by the above
// logic except for the existence of a where clause
while (CanMergeWithFrom(select))
{
SelectExpression fromSelect = (SelectExpression)select.From;
// remove the redundant subquery
select = SubqueryRemover.Remove(select, Logger, fromSelect);
// merge where expressions
Expression where = select.Where;
if (fromSelect.Where != null)
{
if (where != null)
{
where = Expression.And(fromSelect.Where, where);
}
else
{
where = fromSelect.Where;
}
}
if (where != select.Where)
{
select = new SelectExpression(select.Type, select.Alias, select.Columns, select.From, where, select.OrderBy, select.GroupBy);
}
}
return(select);
}
