fix: table preview

@@ -221,3 +221,20 @@ func SelectsExprToMapById(items []SelectExpr) map[string]SelectExpr {
 	}
 	return res
 }
+
+type QueryComponents []*QueryComponent
+
+func (list QueryComponents) IsEmpty(t TableType) bool {
+	if len(list) == 0 {
+		return true
+	}
+	for _, q := range list {
+		switch t {
+		case CalculateTable:
+			if q.Aggregation != nil && len(q.Aggregation.RowFields) == 0 && len(q.Aggregation.ValueFields) == 0 {
+				return true
+			}
+		}
+	}
+	return false
+}

@@ -278,7 +278,7 @@ func (ptr *QuerySetService) PreviewPrepare(ctx *domain.Context, querySetId int,
 			return t, nil
 		}
 	}
-	if len(queryComponents) == 0 {
+	if domain.QueryComponents(queryComponents).IsEmpty(domain.TableType(querySet.Type)) {
 		return &domain.Table{}, nil
 	}