@Override
  public int executeUpdate(String sql) throws SQLException {
    checkConnection("execute update");
    isClosed = false;
    try {
      return executeUpdateSQL(sql);
    } catch (TException e) {
      throw new SQLException(
          "Fail to reconnect to server when execute update " + sql + ". please check server status",
          e);
    }
  }
There are two kinds of sql here: (1) query sql (2) update sql.

<p>(1) return IoTDBJDBCResultSet or IoTDBNonAlignJDBCResultSet (2) simply get executed
iotdb-client/jdbc/src/main/java/org/apache/iotdb/jdbc/IoTDBStatement.java