From da02945e7322db51062e7a137b450a3ef82979cb Mon Sep 17 00:00:00 2001
From: Mark Carrington <31017244+MarkMpn@users.noreply.github.com>
Date: Thu, 25 Jul 2024 08:40:13 +0100
Subject: [PATCH] Do not fold DISTINCT to queries including audit.objectid
 Fixes #519

---
 .../ExecutionPlanTests.cs                     | 27 +++++++++++++++++++
 .../ExecutionPlan/DistinctNode.cs             |  5 ++++
 .../ExecutionPlan/HashJoinNode.cs             |  1 -
 3 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/MarkMpn.Sql4Cds.Engine.Tests/ExecutionPlanTests.cs b/MarkMpn.Sql4Cds.Engine.Tests/ExecutionPlanTests.cs
index ec132dd2..003c2cf1 100644
--- a/MarkMpn.Sql4Cds.Engine.Tests/ExecutionPlanTests.cs
+++ b/MarkMpn.Sql4Cds.Engine.Tests/ExecutionPlanTests.cs
@@ -6040,6 +6040,33 @@ public void SelectAuditObjectId()
                 </fetch>");
         }
 
+        [DataTestMethod]
+        [DataRow("objectid")]
+        [DataRow("objectidname")]
+        [DataRow("objectidtype")]
+        public void SelectAuditObjectIdDistinct(string column)
+        {
+            // https://github.com/MarkMpn/Sql4Cds/issues/296
+            // https://github.com/MarkMpn/Sql4Cds/issues/519
+            // We need to add the objecttypecode attribute to the FetchXML for the first issue, but combining this
+            // with DISTINCT doesn't work because of the second issue.
+            var planBuilder = new ExecutionPlanBuilder(_dataSources.Values, new OptionsWrapper(this) { PrimaryDataSource = "prod" });
+            var query = $"SELECT DISTINCT {column} AS o FROM audit";
+            var plans = planBuilder.Build(query, null, out _);
+
+            Assert.AreEqual(1, plans.Length);
+            var select = AssertNode<SelectNode>(plans[0]);
+            var distinct = AssertNode<DistinctNode>(select.Source);
+            var fetch = AssertNode<FetchXmlScan>(distinct.Source);
+            AssertFetchXml(fetch, @"
+                <fetch xmlns:generator='MarkMpn.SQL4CDS'>
+                    <entity name='audit'>
+                        <attribute name='objectid' />
+                        <attribute name='objecttypecode' />
+                    </entity>
+                </fetch>");
+        }
+
         [TestMethod]
         public void FilterAuditOnLeftJoinColumn()
         {
diff --git a/MarkMpn.Sql4Cds.Engine/ExecutionPlan/DistinctNode.cs b/MarkMpn.Sql4Cds.Engine/ExecutionPlan/DistinctNode.cs
index e55a08f7..017079b0 100644
--- a/MarkMpn.Sql4Cds.Engine/ExecutionPlan/DistinctNode.cs
+++ b/MarkMpn.Sql4Cds.Engine/ExecutionPlan/DistinctNode.cs
@@ -90,6 +90,11 @@ public override IDataExecutionPlanNodeInternal FoldQuery(NodeCompilationContext
 
             if (Source is FetchXmlScan fetch)
             {
+                // Can't apply DISTINCT to audit.objectid
+                // https://github.com/MarkMpn/Sql4Cds/issues/519
+                if (fetch.Entity.name == "audit" && Columns.Any(col => col.StartsWith(fetch.Alias.EscapeIdentifier() + ".objectid")))
+                    return this;
+
                 fetch.FetchXml.distinct = true;
                 fetch.FetchXml.distinctSpecified = true;
                 var metadata = context.DataSources[fetch.DataSource].Metadata;
diff --git a/MarkMpn.Sql4Cds.Engine/ExecutionPlan/HashJoinNode.cs b/MarkMpn.Sql4Cds.Engine/ExecutionPlan/HashJoinNode.cs
index 9de1e78d..cf6c6d95 100644
--- a/MarkMpn.Sql4Cds.Engine/ExecutionPlan/HashJoinNode.cs
+++ b/MarkMpn.Sql4Cds.Engine/ExecutionPlan/HashJoinNode.cs
@@ -200,7 +200,6 @@ public override IDataExecutionPlanNodeInternal FoldQuery(NodeCompilationContext
 
             // Make sure the join keys are not null - the SqlType classes override == to prevent NULL = NULL
             // but .Equals used by the hash table allows them to match
-            // TODO: We do this in the base class as well, can we delete this version?
             if (ComparisonType == BooleanComparisonType.Equals)
             {
                 if (JoinType == QualifiedJoinType.Inner || JoinType == QualifiedJoinType.RightOuter)