class BeamSqlConcatExpression extends BeamSqlExpression {

  @Override
  public boolean accept() {
    if (operands.size() != 2) {
      return false;
    }

    for (BeamSqlExpression exp : getOperands()) {
      if (!SqlTypeName.CHAR_TYPES.contains(exp.getOutputType())) {
        return false;
      }
    }

    return true;
  }

  protected  BeamSqlConcatExpression(List<BeamSqlExpression> operands, SqlTypeName outputType);
  public  BeamSqlConcatExpression(List<BeamSqlExpression> operands);

}