internal static List <SqlSelectExpression> Find(Expression source)
{
var gatherer = new RedundantSubqueryFinder();
gatherer.Visit(source);
return(gatherer.redundant);
}
internal static List<SqlSelectExpression> Find(Expression source)
{
var gatherer = new RedundantSubqueryFinder();
gatherer.Visit(source);
return gatherer.redundant;
}
protected override Expression VisitSelect(SqlSelectExpression select)
{
select = (SqlSelectExpression)base.VisitSelect(select);
// Expand all purely redundant subqueries
var redundantQueries = RedundantSubqueryFinder.Find(select.From);
if (redundantQueries != null)
{
select = SubqueryRemover.Remove(select, redundantQueries);
}
return(select);
}
protected override Expression VisitProjection(SqlProjectionExpression projection)
{
projection = (SqlProjectionExpression)base.VisitProjection(projection);
if (projection.Select.From is SqlSelectExpression)
{
var redundantQueries = RedundantSubqueryFinder.Find(projection.Select);
if (redundantQueries != null)
{
projection = SubqueryRemover.Remove(projection, redundantQueries);
}
}
return(projection);
}
private static bool CanMergeWithFrom(SqlSelectExpression select)
{
var fromSelect = GetLeftMostSelect(select.From);
if (fromSelect == null)
{
return(false);
}
if (!IsColumnProjection(fromSelect))
{
return(false);
}
var selHasNameMapProjection = RedundantSubqueryFinder.IsNameMapProjection(select);
var selHasSkip = select.Skip != null;
var selHasWhere = select.Where != null;
var selHasOrderBy = select.OrderBy != null && select.OrderBy.Count > 0;
var selHasGroupBy = select.GroupBy != null && select.GroupBy.Count > 0;
var selHasAggregates = SqlAggregateChecker.HasAggregates(select);
var frmHasOrderBy = fromSelect.OrderBy != null && fromSelect.OrderBy.Count > 0;
var frmHasGroupBy = fromSelect.GroupBy != null && fromSelect.GroupBy.Count > 0;
// Both cannot have OrderBy
if (selHasOrderBy && frmHasOrderBy)
{
return(false);
}
// Both cannot have GroupBy
if (selHasGroupBy && frmHasGroupBy)
{
return(false);
}
// Cannot move forward OrderBy if outer has GroupBy
if (frmHasOrderBy && (selHasGroupBy || selHasAggregates || select.Distinct))
{
return(false);
}
// Cannot move forward GroupBy if outer has a where clause
if (frmHasGroupBy && (select.Where != null))
{
return(false);
}
// Cannot move forward a take if outer has take or skip or distinct
if (fromSelect.Take != null && (select.Take != null || selHasSkip || select.Distinct || selHasAggregates || selHasGroupBy))
{
return(false);
}
// Cannot move forward a skip if outer has skip or distinct or aggregates with accompanying groupby or where
if (fromSelect.Skip != null && ((selHasWhere || selHasGroupBy) && (select.Skip != null || select.Distinct || selHasAggregates)))
{
return(false);
}
// Cannot merge a distinct if the outer has a distinct or aggregates with accompanying groupby or where
if (fromSelect.Distinct && (!selHasNameMapProjection || (((selHasWhere || selHasGroupBy) && (selHasAggregates || selHasOrderBy)))))
{
return(false);
}
return(true);
}