improve aggregation logic

internal/report/snapshots.go

@@ -664,6 +664,21 @@ func validateTableName(name string) error {
 	return nil
 }
 
+func tableHasRows(ctx context.Context, dbConn *sqlx.DB, table string) (bool, error) {
+	if err := validateTableName(table); err != nil {
+		return false, err
+	}
+	query := fmt.Sprintf(`SELECT 1 FROM %s LIMIT 1`, table)
+	var exists int
+	if err := dbConn.GetContext(ctx, &exists, query); err != nil {
+		if err == sql.ErrNoRows {
+			return false, nil
+		}
+		return false, err
+	}
+	return true, nil
+}
+
 func tableColumns(ctx context.Context, dbConn *sqlx.DB, tableName string) ([]string, error) {
 	driver := strings.ToLower(dbConn.DriverName())
 	switch driver {
@@ -908,6 +923,9 @@ func buildHourlyTotals(ctx context.Context, dbConn *sqlx.DB, records []SnapshotR
 		if err := validateTableName(record.TableName); err != nil {
 			return nil, err
 		}
+		if rowsExist, err := tableHasRows(ctx, dbConn, record.TableName); err != nil || !rowsExist {
+			continue
+		}
 		query := fmt.Sprintf(`
 SELECT
   COUNT(DISTINCT "VmId") AS vm_count,
@@ -955,6 +973,9 @@ func buildDailyTotals(ctx context.Context, dbConn *sqlx.DB, records []SnapshotRe
 		if err := validateTableName(record.TableName); err != nil {
 			return nil, err
 		}
+		if rowsExist, err := tableHasRows(ctx, dbConn, record.TableName); err != nil || !rowsExist {
+			continue
+		}
 		query := fmt.Sprintf(`
 SELECT
   COUNT(DISTINCT "VmId") AS vm_count,