/// <summary>
/// Detects when we can remove order
/// </summary>
/// <param name="selectQuery"></param>
/// <param name="information"></param>
/// <returns></returns>
public static bool TryRemoveDistinct([NotNull] SelectQuery selectQuery, QueryInformation information)
{
if (selectQuery == null)
{
throw new ArgumentNullException(nameof(selectQuery));
}
if (!selectQuery.Select.IsDistinct)
{
return(false);
}
var info = information.GetHierarchyInfo(selectQuery);
switch (info?.HierarchyType)
{
case QueryInformation.HierarchyType.InnerQuery:
{
if (info.ParentElement is SqlFunction func && func.Name == "EXISTS")
{
// ORDER BY not needed for EXISTS function, even when Take and Skip specified
selectQuery.Select.OrderBy.Items.Clear();
if (selectQuery.Select.SkipValue == null && selectQuery.Select.TakeValue == null)
{
// we can sefely remove DISTINCT
selectQuery.Select.IsDistinct = false;
selectQuery.Select.Columns.Clear();
return(true);
}
}
}
break;
}
return(false);
}
/// <summary>
/// Detects when we can remove order
/// </summary>
/// <param name="selectQuery"></param>
/// <param name="flags"></param>
/// <param name="information"></param>
/// <returns></returns>
public static bool CanRemoveOrderBy([NotNull] SelectQuery selectQuery, SqlProviderFlags flags, QueryInformation information)
{
if (selectQuery == null)
{
throw new ArgumentNullException(nameof(selectQuery));
}
if (selectQuery.OrderBy.IsEmpty || selectQuery.ParentSelect == null)
{
return(false);
}
var current = selectQuery;
do
{
if (current.Select.SkipValue != null || current.Select.TakeValue != null)
{
return(false);
}
if (current != selectQuery)
{
if (!current.OrderBy.IsEmpty || current.Select.IsDistinct)
{
return(true);
}
}
var info = information.GetHierarchyInfo(current);
if (info == null)
{
break;
}
switch (info.HierarchyType)
{
case QueryInformation.HierarchyType.From:
if (!flags.IsSubQueryOrderBySupported)
{
return(true);
}
current = info.MasterQuery;
break;
case QueryInformation.HierarchyType.Join:
return(true);
case QueryInformation.HierarchyType.Union:
// currently removing ordering for all UNION
return(true);
case QueryInformation.HierarchyType.InnerQuery:
return(true);
default:
throw new ArgumentOutOfRangeException();
}
} while (current != null);
return(false);
}
