How to solve the pagination issue in shardingjdbc?

Sharding-JDBC is a Java-based distributed database middleware that helps developers quickly implement database sharding and provide pagination functionality.

When using Sharding-JDBC for pagination, you can achieve pagination queries by setting pagination parameters. The specific steps are as follows:

1. First, configure the pagination plugin in the Sharding-JDBC configuration file. You can use the ShardingSphere-provided ShardingPaginationInterceptor plugin, which enables physical pagination functionality.
2. Use PageHelper in the code for pagination queries. PageHelper is a pagination plugin provided by MyBatis, which can intercept query statements and handle pagination.

Here is an example code using Sharding-JDBC for pagination.

public class PaginationExample {

    public static void main(String[] args) {
        // 设置分页参数
        int pageNum = 1; // 当前页码
        int pageSize = 10; // 每页显示的记录数
        
        // 使用PageHelper进行分页
        PageHelper.startPage(pageNum, pageSize);
        
        // 执行查询操作
        List<User> userList = userDao.selectUserList();
        
        // 获取分页结果
        PageInfo<User> pageInfo = new PageInfo<>(userList);
        
        // 输出结果
        System.out.println("总记录数：" + pageInfo.getTotal());
        System.out.println("总页数：" + pageInfo.getPages());
        System.out.println("当前页码：" + pageInfo.getPageNum());
        System.out.println("每页记录数：" + pageInfo.getPageSize());
        System.out.println("查询结果：" + pageInfo.getList());
    }
}

The method PageHelper.startPage(pageNum, pageSize) in the example code above intercepts and processes subsequent query operations for pagination. The pagination result information can be obtained through the PageInfo object.

It’s important to note that due to Sharding-JDBC’s sharding based on physical partitions, there may be limitations when conducting paginated queries. For example, if you need to retrieve the top N records from all shards, you may need to query each shard individually and then merge the results. In this scenario, you can use the BroadcastTableRule provided by Sharding-JDBC to address this issue.

In conclusion, using Sharding-JDBC for pagination queries can be achieved by setting pagination parameters and utilizing pagination plugins. When performing sharded queries, it is essential to be aware of certain limitations and choose the appropriate solution based on the specific circumstances.