// <summary>
// Determines whether an applyNode can be rewritten into a projection with a scalar subquery.
// It can be done if all of the following conditions hold:
// 1. The right child or the apply has only one output
// 2. The right child of the apply produces at most one row
// 3. The right child of the apply produces at least one row, or the Apply operator in question is an OuterApply
// </summary>
private static bool CanRewriteApply(Node rightChild, ExtendedNodeInfo applyRightChildNodeInfo, OpType applyKind)
{
//Check whether it produces only one definition
if (applyRightChildNodeInfo.Definitions.Count != 1)
{
return(false);
}
//Check whether it produces at most one row
if (applyRightChildNodeInfo.MaxRows
!= RowCount.One)
{
return(false);
}
//For cross apply it must also return exactly one row
if (applyKind == OpType.CrossApply &&
(applyRightChildNodeInfo.MinRows != RowCount.One))
{
return(false);
}
//Dev10 #488632: Make sure the right child not only declares to produce only one definition,
// but has exactly one output. For example, ScanTableOp really outputs all the columns from the table,
// but in its ExtendedNodeInfo.Definitions only these that are referenced are shown.
// This is to allow for projection pruning of the unreferenced columns.
if (OutputCountVisitor.CountOutputs(rightChild) != 1)
{
return(false);
}
return(true);
}
// <summary>
// Calculates the number of output columns for the subtree
// rooted at the given node
// </summary>
internal static int CountOutputs(Node node)
{
var visitor = new OutputCountVisitor();
return(visitor.VisitNode(node));
}
