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Fix table variable warnings on modification operators #80

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Merged
erikdarlingdata merged 1 commit into from
Mar 10, 2026
Merged

Fix table variable warnings on modification operators #80

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27 changes: 24 additions & 3 deletions src/PlanViewer.App/Controls/PlanViewerControl.axaml.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -2187,7 +2187,7 @@ private void ShowParameters(PlanStatement statement)

if (parameters.Count == 0)
{
var localVars = FindUnresolvedVariables(statement.StatementText, parameters);
var localVars = FindUnresolvedVariables(statement.StatementText, parameters, statement.RootNode);
if (localVars.Count > 0)
{
ParametersHeader.Text = "Parameters";
Expand Down Expand Up @@ -2303,7 +2303,7 @@ private void ShowParameters(PlanStatement statement)
}
}

var unresolved = FindUnresolvedVariables(statement.StatementText, parameters);
var unresolved = FindUnresolvedVariables(statement.StatementText, parameters, statement.RootNode);
if (unresolved.Count > 0)
{
AddParameterAnnotation(
Expand Down Expand Up @@ -2350,7 +2350,8 @@ private void AddParameterAnnotation(string text, string color)
});
}

private static List<string> FindUnresolvedVariables(string queryText, List<PlanParameter> parameters)
private static List<string> FindUnresolvedVariables(string queryText, List<PlanParameter> parameters,
PlanNode? rootNode = null)
{
var unresolved = new List<string>();
if (string.IsNullOrEmpty(queryText))
Expand All @@ -2359,6 +2360,11 @@ private static List<string> FindUnresolvedVariables(string queryText, List<PlanP
var extractedNames = new HashSet<string>(
parameters.Select(p => p.Name), StringComparer.OrdinalIgnoreCase);

// Collect table variable names from the plan tree so we don't misreport them as local variables
var tableVarNames = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
if (rootNode != null)
CollectTableVariableNames(rootNode, tableVarNames);

var matches = Regex.Matches(queryText, @"@\w+", RegexOptions.IgnoreCase);
var seenVars = new HashSet<string>(StringComparer.OrdinalIgnoreCase);

Expand All @@ -2369,6 +2375,8 @@ private static List<string> FindUnresolvedVariables(string queryText, List<PlanP
continue;
if (varName.StartsWith("@@", StringComparison.OrdinalIgnoreCase))
continue;
if (tableVarNames.Contains(varName))
continue;

seenVars.Add(varName);
unresolved.Add(varName);
Expand All @@ -2377,6 +2385,19 @@ private static List<string> FindUnresolvedVariables(string queryText, List<PlanP
return unresolved;
}

private static void CollectTableVariableNames(PlanNode node, HashSet<string> names)
{
if (!string.IsNullOrEmpty(node.ObjectName) && node.ObjectName.StartsWith("@"))
{
// ObjectName is like "@t.c" — extract the table variable name "@t"
var dotIdx = node.ObjectName.IndexOf('.');
var tvName = dotIdx > 0 ? node.ObjectName[..dotIdx] : node.ObjectName;
names.Add(tvName);
}
foreach (var child in node.Children)
CollectTableVariableNames(child, names);
}

private static void CollectWarnings(PlanNode node, List<PlanWarning> warnings)
{
warnings.AddRange(node.Warnings);
Expand Down
12 changes: 9 additions & 3 deletions src/PlanViewer.Core/Services/PlanAnalyzer.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -388,7 +388,7 @@
var modifiesTableVar = false;
CheckForTableVariables(stmt.RootNode, isModification, ref hasTableVar, ref modifiesTableVar);

if (hasTableVar)
if (hasTableVar && !modifiesTableVar)
{
stmt.PlanWarnings.Add(new PlanWarning
{
Expand Down Expand Up @@ -865,11 +865,17 @@
if (!cfg.IsRuleDisabled(22) && !string.IsNullOrEmpty(node.ObjectName) &&
node.ObjectName.StartsWith("@"))
{
var isModificationOp = node.PhysicalOp.Contains("Insert", StringComparison.OrdinalIgnoreCase)
|| node.PhysicalOp.Contains("Update", StringComparison.OrdinalIgnoreCase)
|| node.PhysicalOp.Contains("Delete", StringComparison.OrdinalIgnoreCase);

node.Warnings.Add(new PlanWarning
{
WarningType = "Table Variable",
Message = "Table variable detected. Table variables lack column-level statistics, which causes bad row estimates, join choices, and memory grant decisions. Replace with a #temp table.",
Severity = PlanWarningSeverity.Warning
Message = isModificationOp
? "Modifying a table variable forces the entire plan to run single-threaded. Replace with a #temp table to allow parallel execution."
: "Table variable detected. Table variables lack column-level statistics, which causes bad row estimates, join choices, and memory grant decisions. Replace with a #temp table.",
Severity = isModificationOp ? PlanWarningSeverity.Critical : PlanWarningSeverity.Warning
});
}

Expand Down Expand Up @@ -943,7 +949,7 @@
// Rule 28: Row Count Spool — NOT IN with nullable column
// Pattern: Row Count Spool with high rewinds, child scan has IS NULL predicate,
// and statement text contains NOT IN
if (!cfg.IsRuleDisabled(28) && node.PhysicalOp.Contains("Row Count Spool"))

Check warning on line 952 in src/PlanViewer.Core/Services/PlanAnalyzer.cs

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GitHub Actions / build-and-test 

Dereference of a possibly null reference.

Check warning on line 952 in src/PlanViewer.Core/Services/PlanAnalyzer.cs

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GitHub Actions / build-and-test 

Dereference of a possibly null reference.
{
var rewinds = node.HasActualStats ? (double)node.ActualRewinds : node.EstimateRewinds;
if (rewinds > 10000 && HasNotInPattern(node, stmt))
Expand Down
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