internal override SqlSource VisitJoin(SqlJoin join)
{
base.VisitJoin(join);
switch (join.JoinType)
{
case SqlJoinType.Cross:
case SqlJoinType.Inner:
// reducing either side would effect cardinality of results
break;
case SqlJoinType.LeftOuter:
case SqlJoinType.CrossApply:
case SqlJoinType.OuterApply:
// may reduce to left if no references to the right
if (this.HasEmptySource(join.Right))
{
SqlAlias a = (SqlAlias)join.Right;
this.removedMap[a] = a;
return(join.Left);
}
break;
}
return(join);
}
internal override SqlSource VisitJoin(SqlJoin join)
{
this.ReferenceColumns(join.Condition);
return(base.VisitJoin(join));
}
internal override SqlSource VisitSource(SqlSource source)
{
source = base.VisitSource(source);
SqlJoin join = source as SqlJoin;
if (join != null)
{
if (join.JoinType == SqlJoinType.OuterApply)
{
// Reduce outer-apply into left-outer-join
HashSet <SqlAlias> leftProducedAliases = SqlGatherProducedAliases.Gather(join.Left);
HashSet <SqlExpression> liftedExpressions = new HashSet <SqlExpression>();
if (SqlPredicateLifter.CanLift(join.Right, leftProducedAliases, liftedExpressions) &&
SqlSelectionLifter.CanLift(join.Right, leftProducedAliases, liftedExpressions) &&
!SqlAliasDependencyChecker.IsDependent(join.Right, leftProducedAliases, liftedExpressions))
{
SqlExpression liftedPredicate = SqlPredicateLifter.Lift(join.Right, leftProducedAliases);
List <List <SqlColumn> > liftedSelections = SqlSelectionLifter.Lift(join.Right, leftProducedAliases, liftedExpressions);
join.JoinType = SqlJoinType.LeftOuter;
join.Condition = liftedPredicate;
if (liftedSelections != null)
{
foreach (List <SqlColumn> selection in liftedSelections)
{
source = this.PushSourceDown(source, selection);
}
}
}
else
{
this.AnnotateSqlIncompatibility(join, SqlProvider.ProviderMode.Sql2000);
}
}
else if (join.JoinType == SqlJoinType.CrossApply)
{
// reduce cross apply with special nested left-outer-join's into a single left-outer-join
//
// SELECT x.*, y.*
// FROM X
// CROSS APPLY (
// SELECT y.*
// FROM (
// SELECT ?
// )
// LEFT OUTER JOIN (
// SELECT y.* FROM Y
// ) AS y
//
// ==>
//
// SELECT x.*, y.*
// FROM X
// LEFT OUTER JOIN (
// SELECT y.* FROM Y
// )
SqlJoin leftOuter = this.GetLeftOuterWithUnreferencedSingletonOnLeft(join.Right);
if (leftOuter != null)
{
HashSet <SqlAlias> leftProducedAliases = SqlGatherProducedAliases.Gather(join.Left);
HashSet <SqlExpression> liftedExpressions = new HashSet <SqlExpression>();
if (SqlPredicateLifter.CanLift(leftOuter.Right, leftProducedAliases, liftedExpressions) &&
SqlSelectionLifter.CanLift(leftOuter.Right, leftProducedAliases, liftedExpressions) &&
!SqlAliasDependencyChecker.IsDependent(leftOuter.Right, leftProducedAliases, liftedExpressions)
)
{
SqlExpression liftedPredicate = SqlPredicateLifter.Lift(leftOuter.Right, leftProducedAliases);
List <List <SqlColumn> > liftedSelections = SqlSelectionLifter.Lift(leftOuter.Right, leftProducedAliases, liftedExpressions);
// add intermediate selections
this.GetSelectionsBeforeJoin(join.Right, liftedSelections);
// push down all selections
foreach (List <SqlColumn> selection in liftedSelections.Where(s => s.Count > 0))
{
source = this.PushSourceDown(source, selection);
}
join.JoinType = SqlJoinType.LeftOuter;
join.Condition = this.factory.AndAccumulate(leftOuter.Condition, liftedPredicate);
join.Right = leftOuter.Right;
}
else
{
this.AnnotateSqlIncompatibility(join, SqlProvider.ProviderMode.Sql2000);
}
}
}
// re-balance join tree of left-outer-joins to expose LOJ w/ leftside unreferenced
while (join.JoinType == SqlJoinType.LeftOuter)
{
// look for buried left-outer-joined-with-unreferenced singleton
SqlJoin leftLeftOuter = this.GetLeftOuterWithUnreferencedSingletonOnLeft(join.Left);
if (leftLeftOuter == null)
{
break;
}
List <List <SqlColumn> > liftedSelections = new List <List <SqlColumn> >();
// add intermediate selections
this.GetSelectionsBeforeJoin(join.Left, liftedSelections);
// push down all selections
foreach (List <SqlColumn> selection in liftedSelections)
{
source = this.PushSourceDown(source, selection);
}
// bubble this one up on-top of this 'join'.
SqlSource jRight = join.Right;
SqlExpression jCondition = join.Condition;
join.Left = leftLeftOuter.Left;
join.Right = leftLeftOuter;
join.Condition = leftLeftOuter.Condition;
leftLeftOuter.Left = leftLeftOuter.Right;
leftLeftOuter.Right = jRight;
leftLeftOuter.Condition = jCondition;
}
}
return(source);
}
