Only convert join to nested loop if inner filter can be folded

MarkMpn · Mar 4, 2022 · 8949677 · 8949677
1 parent 813089b
commit 8949677
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Showing 2 changed files with 21 additions and 13 deletions.
diff --git a/MarkMpn.Sql4Cds.Engine.Tests/ExecutionPlanTests.cs b/MarkMpn.Sql4Cds.Engine.Tests/ExecutionPlanTests.cs
@@ -3868,7 +3868,6 @@ public void MetadataLeftJoinData()
                         <filter>
                             <condition attribute='accountid' operator='eq' value='@Cond1' />
                         </filter>
-                        <order attribute='accountid' />
                     </entity>
                 </fetch>");
             var contactFetch = AssertNode<FetchXmlScan>(nestedLoop1.RightSource);
@@ -3879,7 +3878,6 @@ public void MetadataLeftJoinData()
                         <filter>
                             <condition attribute='contactid' operator='eq' value='@Cond2' />
                         </filter>
-                        <order attribute='contactid' />
                     </entity>
                 </fetch>");
         }

diff --git a/MarkMpn.Sql4Cds.Engine/ExecutionPlan/FoldableJoinNode.cs b/MarkMpn.Sql4Cds.Engine/ExecutionPlan/FoldableJoinNode.cs
@@ -322,27 +322,37 @@ private bool FoldSingleRowJoinToNestedLoop(IDictionary<string, DataSource> dataS
             if (leftSource.EstimatedRowsOut > 1)
                 return false;
 
+            // Add the filter to the inner side of the nested loop
             var outerReference = $"@Cond{++_nestedLoopCount}";
+            var filteredRightSource = new FilterNode
+            {
+                Source = rightSource,
+                Filter = new BooleanComparisonExpression
+                {
+                    FirstExpression = rightAttribute,
+                    ComparisonType = BooleanComparisonType.Equals,
+                    SecondExpression = new VariableReference { Name = outerReference }
+                }
+            };
+            var foldedRightSource = filteredRightSource.FoldQuery(dataSources, options, parameterTypes, hints);
+
+            // If we can't fold the filter down to the data source, there's no benefit from doing this so stick with the
+            // original join type
+            if (foldedRightSource == filteredRightSource)
+                return false;
+
             var nestedLoop = new NestedLoopNode
             {
                 JoinType = joinType,
                 LeftSource = leftSource,
-                RightSource = new FilterNode
-                {
-                    Source = rightSource,
-                    Filter = new BooleanComparisonExpression
-                    {
-                        FirstExpression = rightAttribute,
-                        ComparisonType = BooleanComparisonType.Equals,
-                        SecondExpression = new VariableReference { Name = outerReference }
-                    }
-                },
+                RightSource = foldedRightSource,
                 OuterReferences = new Dictionary<string, string>
                 {
                     [leftAttr] = outerReference
                 }
             };
 
+            // Merge joins might have added sorts already. They're not needed any longer, so remove them.
             if (nestedLoop.LeftSource is SortNode leftSort)
                 nestedLoop.LeftSource = leftSort.Source;
             else if (nestedLoop.LeftSource is FetchXmlScan leftFetch)
@@ -353,7 +363,7 @@ private bool FoldSingleRowJoinToNestedLoop(IDictionary<string, DataSource> dataS
             else if (nestedLoop.RightSource is FetchXmlScan rightFetch)
                 rightFetch.RemoveSorts();
 
-            folded = nestedLoop.FoldQuery(dataSources, options, parameterTypes, hints);
+            folded = nestedLoop;
             return true;
         }