SQL Expressions / Alerting: Do not allow duplicates (#103394)

pkg/expr/sql_command.go

@@ -182,6 +182,20 @@ func totalCells(frames []*data.Frame) (total int64) {
 	return
 }
 
+// extractNumberSetFromSQLForAlerting converts a data frame produced by a SQL expression
+// into a slice of mathexp.Number values for use in alerting.
+//
+// This function enforces strict semantics: each row must have exactly one numeric value
+// and a unique label set. If any label set appears more than once, an error is returned.
+//
+// It is the responsibility of the SQL query to ensure uniqueness — for example, by
+// applying GROUP BY or aggregation clauses. This function will not deduplicate rows;
+// it will reject the entire input if any duplicates are present.
+//
+// Returns an error if:
+//   - No numeric field is found.
+//   - More than one numeric field exists.
+//   - Any label set appears more than once.
 func extractNumberSetFromSQLForAlerting(frame *data.Frame) ([]mathexp.Number, error) {
 	var (
 		numericField   *data.Field
@@ -202,7 +216,13 @@ func extractNumberSetFromSQLForAlerting(frame *data.Frame) ([]mathexp.Number, er
 		return nil, fmt.Errorf("no numeric field found in frame")
 	}
 
-	numbers := make([]mathexp.Number, frame.Rows())
+	type row struct {
+		value  float64
+		labels data.Labels
+	}
+	rows := make([]row, 0, frame.Rows())
+	counts := map[data.Fingerprint]int{}
+	labelMap := map[data.Fingerprint]string{}
 
 	for i := 0; i < frame.Rows(); i++ {
 		val, err := numericField.FloatAt(i)
@@ -227,10 +247,32 @@ func extractNumberSetFromSQLForAlerting(frame *data.Frame) ([]mathexp.Number, er
 			}
 		}
 
-		n := mathexp.NewNumber(numericField.Name, labels)
+		fp := labels.Fingerprint()
+		counts[fp]++
+		labelMap[fp] = labels.String()
+
+		rows = append(rows, row{value: val, labels: labels})
+	}
+
+	// Check for any duplicates
+	duplicates := make([]string, 0)
+	for fp, count := range counts {
+		if count > 1 {
+			duplicates = append(duplicates, labelMap[fp])
+		}
+	}
+
+	if len(duplicates) > 0 {
+		return nil, makeDuplicateStringColumnError(duplicates)
+	}
+
+	// Build final result
+	numbers := make([]mathexp.Number, 0, len(rows))
+	for _, r := range rows {
+		n := mathexp.NewNumber(numericField.Name, r.labels)
 		n.Frame.Fields[0].Config = numericField.Config
-		n.SetValue(&val)
-		numbers[i] = n
+		n.SetValue(&r.value)
+		numbers = append(numbers, n)
 	}
 
 	return numbers, nil