// <summary>
// Converts a Apply(X,Y) => Project(X, Y1), where Y1 is a scalar subquery version of Y
// The transformation is valid only if all of the following conditions hold:
// 1. Y produces only one output
// 2. Y produces at most one row
// 3. Y produces at least one row, or the Apply operator in question is an OuterApply
// </summary>
// <param name="context"> Rule processing context </param>
// <param name="applyNode"> The ApplyOp subtree </param>
// <param name="newNode"> transformed subtree </param>
// <returns> the transformation status </returns>
private static bool ProcessApplyIntoScalarSubquery(RuleProcessingContext context, Node applyNode, out Node newNode)
{
var command = context.Command;
var applyRightChildNodeInfo = command.GetExtendedNodeInfo(applyNode.Child1);
var applyKind = applyNode.Op.OpType;
if (!CanRewriteApply(applyNode.Child1, applyRightChildNodeInfo, applyKind))
{
newNode = applyNode;
return(false);
}
// Create the project node over the original input with element over the apply as new projected var
var applyLeftChildNodeInfo = command.GetExtendedNodeInfo(applyNode.Child0);
var oldVar = applyRightChildNodeInfo.Definitions.First;
// Project all the outputs from the left child
var projectOpOutputs = command.CreateVarVec(applyLeftChildNodeInfo.Definitions);
//
// Remap the var defining tree to get it into a consistent state
// and then remove all references to oldVar from it to avoid them being wrongly remapped to newVar
// in subsequent remappings.
//
var trc = (TransformationRulesContext)context;
trc.RemapSubtree(applyNode.Child1);
VarDefinitionRemapper.RemapSubtree(applyNode.Child1, command, oldVar);
var elementNode = command.CreateNode(command.CreateElementOp(oldVar.Type), applyNode.Child1);
Var newVar;
var varDefListNode = command.CreateVarDefListNode(elementNode, out newVar);
projectOpOutputs.Set(newVar);
newNode = command.CreateNode(
command.CreateProjectOp(projectOpOutputs),
applyNode.Child0,
varDefListNode);
// Add the var mapping from oldVar to newVar
trc.AddVarMapping(oldVar, newVar);
return(true);
}
// <summary>
// Public entry point.
// Remaps the subtree rooted at the given tree
// </summary>
internal static void RemapSubtree(Node root, Command command, Var oldVar)
{
var remapper = new VarDefinitionRemapper(oldVar, command);
remapper.RemapSubtree(root);
}