/// <summary>
/// Split up a predicate into 2 parts - the pushdown and the non-pushdown predicate.
///
/// If the filter node has no external references *and* the "columns" parameter is null,
/// then the entire predicate can be pushed down
///
/// We then compute the set of valid column references - if the "columns" parameter
/// is non-null, this set is used. Otherwise, we get the definitions of the
/// input relop node of the filterOp, and use that.
///
/// We use this list of valid column references to identify which parts of the filter
/// predicate can be pushed down - only those parts of the predicate that do not
/// reference anything beyond these columns are considered for pushdown. The rest are
/// stuffed into the nonPushdownPredicate output parameter
///
/// </summary>
/// <param name="command">Command object</param>
/// <param name="filterNode">the FilterOp subtree</param>
/// <param name="columns">(Optional) List of columns to consider for "pushdown"</param>
/// <param name="nonPushdownPredicateNode">(output) Part of the predicate that cannot be pushed down</param>
/// <returns>part of the predicate that can be pushed down</returns>
private static Node GetPushdownPredicate(Command command, Node filterNode, VarVec columns, out Node nonPushdownPredicateNode)
{
var pushdownPredicateNode = filterNode.Child1;
nonPushdownPredicateNode = null;
var filterNodeInfo = command.GetExtendedNodeInfo(filterNode);
if (columns == null
&& filterNodeInfo.ExternalReferences.IsEmpty)
{
return pushdownPredicateNode;
}
if (columns == null)
{
var inputNodeInfo = command.GetExtendedNodeInfo(filterNode.Child0);
columns = inputNodeInfo.Definitions;
}
var predicate = new Predicate(command, pushdownPredicateNode);
Predicate nonPushdownPredicate;
predicate = predicate.GetSingleTablePredicates(columns, out nonPushdownPredicate);
pushdownPredicateNode = predicate.BuildAndTree();
nonPushdownPredicateNode = nonPushdownPredicate.BuildAndTree();
return pushdownPredicateNode;
}
private static bool ProcessFilterOverJoin(RuleProcessingContext context, Node filterNode, out Node newNode)
{
newNode = filterNode;
var trc = (TransformationRulesContext)context;
//
// Have we shut off filter pushdown for this node? Return
//
if (trc.IsFilterPushdownSuppressed(filterNode))
{
return false;
}
var joinNode = filterNode.Child0;
var joinOp = joinNode.Op;
var leftInputNode = joinNode.Child0;
var rightInputNode = joinNode.Child1;
var command = trc.Command;
var needsTransformation = false;
//
// If we're dealing with an outer-join, first check to see if the current
// predicate preserves nulls for the right table.
// If it doesn't then we can convert the outer join into an inner join,
// and then continue with the rest of our processing here
//
var rightTableNodeInfo = command.GetExtendedNodeInfo(rightInputNode);
var predicate = new Predicate(command, filterNode.Child1);
if (joinOp.OpType
== OpType.LeftOuterJoin)
{
if (!predicate.PreservesNulls(rightTableNodeInfo.Definitions, true))
{
joinOp = command.CreateInnerJoinOp();
needsTransformation = true;
}
}
var leftTableInfo = command.GetExtendedNodeInfo(leftInputNode);
//
// Check to see if the predicate contains any "single-table-filters". In those
// cases, we could simply push that filter down to the child.
// We can do this for inner joins and cross joins - for both inputs.
// For left-outer joins, however, we can only do this for the left-side input
// Further note that we only want to do the pushdown if it will help us - if
// the join input is a ScanTable (or some other cases), then it doesn't help us.
//
Node leftSingleTablePredicateNode = null;
if (leftInputNode.Op.OpType
!= OpType.ScanTable)
{
var leftSingleTablePredicates = predicate.GetSingleTablePredicates(leftTableInfo.Definitions, out predicate);
leftSingleTablePredicateNode = leftSingleTablePredicates.BuildAndTree();
}
Node rightSingleTablePredicateNode = null;
if ((rightInputNode.Op.OpType != OpType.ScanTable)
&&
(joinOp.OpType != OpType.LeftOuterJoin))
{
var rightSingleTablePredicates = predicate.GetSingleTablePredicates(rightTableNodeInfo.Definitions, out predicate);
rightSingleTablePredicateNode = rightSingleTablePredicates.BuildAndTree();
}
//
// Now check to see if the predicate contains some "join predicates". We can
// add these to the existing join predicate (if any).
// We can only do this for inner joins and cross joins - not for LOJs
//
Node newJoinPredicateNode = null;
if (joinOp.OpType == OpType.CrossJoin
|| joinOp.OpType == OpType.InnerJoin)
{
var joinPredicate = predicate.GetJoinPredicates(leftTableInfo.Definitions, rightTableNodeInfo.Definitions, out predicate);
newJoinPredicateNode = joinPredicate.BuildAndTree();
}
//
// Now for the dirty work. We've identified some predicates that could be pushed
// into the left table, some predicates that could be pushed into the right table
// and some that could become join predicates.
//
if (leftSingleTablePredicateNode != null)
{
leftInputNode = command.CreateNode(command.CreateFilterOp(), leftInputNode, leftSingleTablePredicateNode);
needsTransformation = true;
}
if (rightSingleTablePredicateNode != null)
{
rightInputNode = command.CreateNode(command.CreateFilterOp(), rightInputNode, rightSingleTablePredicateNode);
needsTransformation = true;
}
// Identify the new join predicate
if (newJoinPredicateNode != null)
{
needsTransformation = true;
if (joinOp.OpType
== OpType.CrossJoin)
{
joinOp = command.CreateInnerJoinOp();
}
else
{
PlanCompiler.Assert(joinOp.OpType == OpType.InnerJoin, "unexpected non-InnerJoin?");
newJoinPredicateNode = PlanCompilerUtil.CombinePredicates(joinNode.Child2, newJoinPredicateNode, command);
}
}
else
{
newJoinPredicateNode = (joinOp.OpType == OpType.CrossJoin) ? null : joinNode.Child2;
}
//
// If nothing has changed, then just return the current node. Otherwise,
// we will loop forever
//
if (!needsTransformation)
{
return false;
}
Node newJoinNode;
//
// Finally build up a new join node
//
if (joinOp.OpType
== OpType.CrossJoin)
{
newJoinNode = command.CreateNode(joinOp, leftInputNode, rightInputNode);
}
else
{
newJoinNode = command.CreateNode(joinOp, leftInputNode, rightInputNode, newJoinPredicateNode);
}
//
// Build up a new filterNode above this join node. But only if we have a filter left
//
var newFilterPredicateNode = predicate.BuildAndTree();
if (newFilterPredicateNode == null)
{
newNode = newJoinNode;
}
else
{
newNode = command.CreateNode(command.CreateFilterOp(), newJoinNode, newFilterPredicateNode);
}
return true;
}