@Override
  public void setMaxRows(int num) throws SQLException {
    checkConnection("setMaxRows");
    if (num < 0) {
      throw new SQLException(String.format("maxRows %d must be >= 0!", num));
    }
    this.maxRows = num;
  }
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