adjusted handling of zero-rows results (#121)

Author: gabor

dataframe_test.go

@@ -40,7 +40,7 @@ func TestNoRowsFrame(t *testing.T) {
 				},
 				Rows: [][]any{},
 			},
-			expectedFieldCount: 0,
+			expectedFieldCount: 2,
 		},
 		{
 			name:   "empty wide",
@@ -135,7 +135,7 @@ func TestNoRowsFrame(t *testing.T) {
 				},
 				Rows: [][]any{},
 			},
-			expectedFieldCount: 0,
+			expectedFieldCount: 2,
 		},
 		{
 			name:   "trace",
@@ -151,7 +151,7 @@ func TestNoRowsFrame(t *testing.T) {
 				},
 				Rows: [][]any{},
 			},
-			expectedFieldCount: 0,
+			expectedFieldCount: 1,
 		},
 	}
 

query.go

@@ -131,15 +131,19 @@ func getFrames(rows *sql.Rows, limit int64, converters []sqlutil.Converter, fill
 	if err != nil {
 		return nil, err
 	}
-	if count == 0 {
-		return nil, ErrorNoResults
-	}
+
+	// the handling of zero-rows differs between various "format"s.
+	zeroRows := count == 0
 
 	frame.Meta.ExecutedQueryString = query.RawSQL
 	frame.Meta.PreferredVisualization = data.VisTypeGraph
 
 	switch query.Format {
 	case FormatOptionMulti:
+		if zeroRows {
+			return nil, ErrorNoResults
+		}
+
 		if frame.TimeSeriesSchema().Type == data.TimeSeriesTypeLong {
 
 			err = fixFrameForLongToMulti(frame)
@@ -161,6 +165,10 @@ func getFrames(rows *sql.Rows, limit int64, converters []sqlutil.Converter, fill
 		frame.Meta.PreferredVisualization = data.VisTypeTrace
 	// Format as timeSeries
 	default:
+		if zeroRows {
+			return nil, ErrorNoResults
+		}
+
 		if frame.TimeSeriesSchema().Type == data.TimeSeriesTypeLong {
 			frame, err = data.LongToWide(frame, fillMode)
 			if err != nil {