From 5c3134c394659ec0965e187ef4650ca7d4e19629 Mon Sep 17 00:00:00 2001
From: Mark Carrington <MarkMpn@users.noreply.github.com>
Date: Wed, 6 Apr 2022 08:54:40 +0100
Subject: [PATCH] Fold conditional query for IF/WHILE statements Remove
 unnecessary table spool for EXISTS

---
 .../ExecutionPlanTests.cs                     | 42 +++++++++++++++++++
 .../ExecutionPlan/ConditionalNode.cs          | 30 +++++++------
 .../ExecutionPlan/NestedLoopNode.cs           | 11 +++++
 3 files changed, 67 insertions(+), 16 deletions(-)

diff --git a/MarkMpn.Sql4Cds.Engine.Tests/ExecutionPlanTests.cs b/MarkMpn.Sql4Cds.Engine.Tests/ExecutionPlanTests.cs
index e588098a..c80181e5 100644
--- a/MarkMpn.Sql4Cds.Engine.Tests/ExecutionPlanTests.cs
+++ b/MarkMpn.Sql4Cds.Engine.Tests/ExecutionPlanTests.cs
@@ -4212,5 +4212,47 @@ public void InsertParameters()
             var compute = AssertNode<ComputeScalarNode>(insert.Source);
             var constant = AssertNode<ConstantScanNode>(compute.Source);
         }
+
+        [TestMethod]
+        public void NotExistsParameters()
+        {
+            var metadata = new AttributeMetadataCache(_service);
+            var planBuilder = new ExecutionPlanBuilder(metadata, new StubTableSizeCache(), this);
+
+            var query = @"DECLARE @firstname AS VARCHAR (100) = 'Mark', @lastname AS VARCHAR (100) = 'Carrington';
+
+IF NOT EXISTS (SELECT * FROM contact WHERE firstname = @firstname AND lastname = @lastname)
+BEGIN
+    INSERT INTO contact (firstname, lastname)
+    VALUES              (@firstname, @lastname);
+END";
+
+            var plans = planBuilder.Build(query, null, out _);
+
+            Assert.AreEqual(4, plans.Length);
+
+            AssertNode<DeclareVariablesNode>(plans[0]);
+            AssertNode<AssignVariablesNode>(plans[1]);
+            AssertNode<AssignVariablesNode>(plans[2]);
+            var cond = AssertNode<ConditionalNode>(plans[3]);
+            var compute = AssertNode<ComputeScalarNode>(cond.Source);
+            var loop = AssertNode<NestedLoopNode>(compute.Source);
+            var constant = AssertNode<ConstantScanNode>(loop.LeftSource);
+            var fetch = AssertNode<FetchXmlScan>(loop.RightSource);
+            var insert = AssertNode<InsertNode>(cond.TrueStatements[0]);
+            var insertCompute = AssertNode<ComputeScalarNode>(insert.Source);
+            var insertConstant = AssertNode<ConstantScanNode>(insertCompute.Source);
+
+            AssertFetchXml(fetch, @"
+                <fetch xmlns:generator='MarkMpn.SQL4CDS' top='1'>
+                    <entity name='contact'>
+                        <attribute name='contactid' />
+                        <filter>
+                            <condition attribute='firstname' operator='eq' value='@firstname' generator:IsVariable='true' />
+                            <condition attribute='lastname' operator='eq' value='@lastname' generator:IsVariable='true' />
+                        </filter>
+                    </entity>
+                </fetch>");
+        }
     }
 }
diff --git a/MarkMpn.Sql4Cds.Engine/ExecutionPlan/ConditionalNode.cs b/MarkMpn.Sql4Cds.Engine/ExecutionPlan/ConditionalNode.cs
index e1d9914f..c147d3fc 100644
--- a/MarkMpn.Sql4Cds.Engine/ExecutionPlan/ConditionalNode.cs
+++ b/MarkMpn.Sql4Cds.Engine/ExecutionPlan/ConditionalNode.cs
@@ -69,24 +69,24 @@ public string Execute(IDictionary<string, DataSource> dataSources, IQueryExecuti
 
         public IRootExecutionPlanNodeInternal[] FoldQuery(IDictionary<string, DataSource> dataSources, IQueryExecutionOptions options, IDictionary<string, DataTypeReference> parameterTypes, IList<OptimizerHint> hints)
         {
-            if (hints != null && hints.OfType<DoNotCompileConditionsHint>().Any())
-            {
-                TrueStatements = TrueStatements
-                    .SelectMany(s => s.FoldQuery(dataSources, options, parameterTypes, hints))
-                    .ToArray();
+            TrueLabel = Guid.NewGuid().ToString();
+            FalseLabel = Guid.NewGuid().ToString();
 
-                FalseStatements = FalseStatements
-                    ?.SelectMany(s => s.FoldQuery(dataSources, options, parameterTypes, hints))
-                    ?.ToArray();
+            Source = Source?.FoldQuery(dataSources, options, parameterTypes, hints);
 
+            TrueStatements = TrueStatements
+                .SelectMany(s => s.FoldQuery(dataSources, options, parameterTypes, hints))
+                .ToArray();
+
+            FalseStatements = FalseStatements
+                ?.SelectMany(s => s.FoldQuery(dataSources, options, parameterTypes, hints))
+                ?.ToArray();
+
+            if (hints != null && hints.OfType<DoNotCompileConditionsHint>().Any())
                 return new[] { this };
-            }
 
             var statements = new List<IRootExecutionPlanNodeInternal>();
 
-            TrueLabel = Guid.NewGuid().ToString();
-            FalseLabel = Guid.NewGuid().ToString();
-
             statements.AddRange(
                 new GoToNode
                 {
@@ -104,8 +104,7 @@ public IRootExecutionPlanNodeInternal[] FoldQuery(IDictionary<string, DataSource
 
             statements.Add(new GotoLabelNode { Label = TrueLabel });
 
-            foreach (var stmt in TrueStatements)
-                statements.AddRange(stmt.FoldQuery(dataSources, options, parameterTypes, hints));
+            statements.AddRange(TrueStatements);
 
             if (FalseStatements == null)
             {
@@ -134,8 +133,7 @@ public IRootExecutionPlanNodeInternal[] FoldQuery(IDictionary<string, DataSource
 
                 statements.Add(new GotoLabelNode { Label = FalseLabel });
 
-                foreach (var stmt in FalseStatements)
-                    statements.AddRange(stmt.FoldQuery(dataSources, options, parameterTypes, hints));
+                statements.AddRange(FalseStatements);
 
                 statements.Add(new GotoLabelNode { Label = endLabel });
             }
diff --git a/MarkMpn.Sql4Cds.Engine/ExecutionPlan/NestedLoopNode.cs b/MarkMpn.Sql4Cds.Engine/ExecutionPlan/NestedLoopNode.cs
index 00c7275d..c0f98426 100644
--- a/MarkMpn.Sql4Cds.Engine/ExecutionPlan/NestedLoopNode.cs
+++ b/MarkMpn.Sql4Cds.Engine/ExecutionPlan/NestedLoopNode.cs
@@ -114,6 +114,17 @@ public override IDataExecutionPlanNodeInternal FoldQuery(IDictionary<string, Dat
             var innerParameterTypes = GetInnerParameterTypes(leftSchema, parameterTypes);
             RightSource = RightSource.FoldQuery(dataSources, options, innerParameterTypes, hints);
             RightSource.Parent = this;
+
+            if (RightSource is TableSpoolNode spool)
+            {
+                LeftSource.EstimateRowsOut(dataSources, options, parameterTypes);
+                if (LeftSource.EstimatedRowsOut <= 1)
+                {
+                    RightSource = spool.Source;
+                    RightSource.Parent = this;
+                }
+            }
+
             return this;
         }