fix(aggregation): if summing or averaging over nothing, we should return zero

Author: thesophiaxu

query/aggregator.go

@@ -601,7 +601,17 @@ func (ag *aggregator) divideByCount() {
 
 func (ag *aggregator) Value() (types.Val, error) {
 	if ag.result.Value == nil {
-		return ag.result, ErrEmptyVal
+		if ag.name == "avg" || ag.name == "sum" {
+			switch {
+			case ag.result.Tid != types.FloatID:
+				ag.result.Tid = types.IntID
+				ag.result.Value = int64(0)
+			case ag.result.Tid == types.FloatID:
+				ag.result.Value = float64(0)
+			}
+		} else {
+			return ag.result, ErrEmptyVal
+		}
 	}
 	ag.divideByCount()
 	if ag.result.Tid == types.FloatID {

query/query1_test.go

@@ -1486,7 +1486,7 @@ func TestAggregateRoot5(t *testing.T) {
 		}
 	`
 	js := processQueryNoErr(t, query)
-	require.JSONEq(t, `{"data": {"me":[{"sum(val(m))":null}]}}`, js)
+	require.JSONEq(t, `{"data": {"me":[{"sum(val(m))":0}]}}`, js)
 }
 
 func TestAggregateRoot6(t *testing.T) {
@@ -1548,7 +1548,7 @@ func TestAggregateEmptyData(t *testing.T) {
 		}
 	`
 	js := processQueryNoErr(t, query)
-	require.JSONEq(t, `{"data": {"me":[{"avg(val(a))":null},{"min(val(a))":null},{"max(val(a))":null}]}}`, js)
+	require.JSONEq(t, `{"data": {"me":[{"avg(val(a))":0},{"min(val(a))":null},{"max(val(a))":null}]}}`, js)
 }
 
 func TestCountEmptyData(t *testing.T) {