private AlgebraNode PushOverJoin(FilterAlgebraNode node)
{
JoinAlgebraNode inputNode = (JoinAlgebraNode)node.Input;
// Get declared tables of left and right
RowBufferEntry[] leftDefinedValues = AstUtil.GetDefinedValueEntries(inputNode.Left);
RowBufferEntry[] rightDefinedValues = AstUtil.GetDefinedValueEntries(inputNode.Right);
// Obviously, we cannot merge the filter with the join if the join is an outer join
// (since it would change the join's semantics).
//
// Another less obvious restriction is that we cannot merge a filter with the join if
// the join has a passthru predicate. In case the passthru predicte evaluates to true
// the filter would not be applied. However, we are allowed to push the filter the over
// join.
bool canMerge = inputNode.Op != JoinAlgebraNode.JoinOperator.FullOuterJoin &&
inputNode.Op != JoinAlgebraNode.JoinOperator.LeftOuterJoin &&
inputNode.Op != JoinAlgebraNode.JoinOperator.RightOuterJoin &&
inputNode.PassthruPredicate == null;
if (canMerge)
{
// We can merge the filter with the condition of the join.
//
// However, we have to make sure that the predicate does not reference the probe column.
// Since not having a probe column is the most common case, we don't always split the
// predicate into conjuncts.
if (inputNode.ProbeBufferEntry == null || !ArrayHelpers.Contains(AstUtil.GetRowBufferEntryReferences(node.Predicate), inputNode.ProbeBufferEntry))
{
// Either there is no probe column defined or the filter does not reference it. That means
// no splitting necessary, we can just merge the whole predicate with the join predicate.
inputNode.Predicate = AstUtil.CombineConditions(LogicalOperator.And, inputNode.Predicate, node.Predicate);
return(VisitAlgebraNode(inputNode));
}
else
{
// Unfortunately, the filter references the probe column. Now let's check whether we can merge
// conjuncts of the predicate.
List <ExpressionNode> remainingAndParts = new List <ExpressionNode>();
List <ExpressionNode> mergableAndParts = new List <ExpressionNode>();
foreach (ExpressionNode andPart in AstUtil.SplitCondition(LogicalOperator.And, node.Predicate))
{
bool andPartReferencesProbeColumn = ArrayHelpers.Contains(AstUtil.GetRowBufferEntryReferences(andPart), inputNode.ProbeBufferEntry);
if (andPartReferencesProbeColumn)
{
remainingAndParts.Add(andPart);
}
else
{
mergableAndParts.Add(andPart);
}
}
if (mergableAndParts.Count > 0)
{
ExpressionNode combinedMergableAndParts = AstUtil.CombineConditions(LogicalOperator.And, mergableAndParts.ToArray());
inputNode.Predicate = AstUtil.CombineConditions(LogicalOperator.And, inputNode.Predicate, combinedMergableAndParts);
node.Predicate = AstUtil.CombineConditions(LogicalOperator.And, remainingAndParts);
if (node.Predicate == null)
{
return(VisitAlgebraNode(inputNode));
}
}
}
}
else
{
// The condition cannot be merged. Now we try to push AND-parts over the join.
List <ExpressionNode> leftAndParts = new List <ExpressionNode>();
List <ExpressionNode> rightAndParts = new List <ExpressionNode>();
List <ExpressionNode> remainingAndParts = new List <ExpressionNode>();
foreach (ExpressionNode andPart in AstUtil.SplitCondition(LogicalOperator.And, node.Predicate))
{
bool andPartReferencesProbeColumn = inputNode.ProbeBufferEntry != null &&
ArrayHelpers.Contains(AstUtil.GetRowBufferEntryReferences(andPart), inputNode.ProbeBufferEntry);
if (!andPartReferencesProbeColumn && AstUtil.AllowsLeftPushOver(inputNode.Op) && AstUtil.ExpressionDoesNotReference(andPart, rightDefinedValues))
{
// The AND-part depends only on the LHS and the join is inner/left.
// So we are allowed to push this AND-part down.
leftAndParts.Add(andPart);
}
else if (!andPartReferencesProbeColumn && AstUtil.AllowsRightPushOver(inputNode.Op) && AstUtil.ExpressionDoesNotReference(andPart, leftDefinedValues))
{
// The AND-part depends only on the RHS and the join is inner/right.
// So we are allowed to push this AND-part down.
rightAndParts.Add(andPart);
}
else
{
remainingAndParts.Add(andPart);
}
}
if (leftAndParts.Count > 0)
{
inputNode.Left = GetFilterFromAndParts(leftAndParts, inputNode.Left);
}
if (rightAndParts.Count > 0)
{
inputNode.Right = GetFilterFromAndParts(rightAndParts, inputNode.Right);
}
node.Predicate = AstUtil.CombineConditions(LogicalOperator.And, remainingAndParts);
if (node.Predicate == null)
{
return(VisitAlgebraNode(inputNode));
}
}
node.Input = VisitAlgebraNode(node.Input);
return(node);
}