The result list return wrong size when there's limit sub clause for single routing

[caedmonz]

Bug Report

Which version of ShardingSphere did you use?

3.1.0.M1

Which project did you use? Sharding-JDBC or Sharding-Proxy?

Sharding-JDBC

Expected behavior

The SQL is single routed to t_order0;
origin data:
order_id: 1, status: 1
order_id: 1, status: 2
order_id: 1, status: 3
order_id: 1, status: 4

SELECT * FROM t_order WHERE user_id = 0 LIMIT ?, ?;
My programe set two params as 1,2 with PreparedStatement

expexted:
order_id: 1, status: 2
order_id: 1, status: 3

Actual behavior

order_id: 1, status: 1
order_id: 1, status: 2
order_id: 1, status: 3

Reason analyze (If you can)

ParsingSQLRouter will override limit and offset even if the SQL is single routed. However, DQLMergeEngine will not merge result when queryResult size is just one.
100% compatible（MySQL only, other database dialect is doing) . Thus, there should not have any override operation when single routed.

Steps to reproduce the behavior, such as: SQL to execute, sharding rule configuration, when exception occur etc.

String sql = "SELECT id, order_id, status FROM t_order where order_id = 1 limit ?,?";
DataSource dataSource = ShardingDataSource.makeShardingDataSource();
Connection connection = dataSource.getConnection();
PreparedStatement preparedStatement = connection.prepareStatement(sql);

preparedStatement.setInt(1, 1);
preparedStatement.setInt(2, 2);
ResultSet resultSet = preparedStatement.executeQuery();

Example codes for reproduce this issue (such as a github link).

[tuohai666]

Known issue.
Please refer to #1672 and #1722