方案一：使用mybatis-plus原生加载

服务类中的查询方法如下.

    public void findAll(){
        QueryWrapper<DailyAmt> queryWrapper=new QueryWrapper<>();
        queryWrapper.select("check_date","hosp_id","yesterday_amt","recharge_amt","payment_amt");
        long startDateTime=System.currentTimeMillis();
        List<DailyAmt> list=list(queryWrapper);
        long endDateTIme=System.currentTimeMillis();
        log.info("【查询日金额表所有数据】消耗时间:{}",(endDateTIme-startDateTime));
    }

执行结果：总数据217万5872条，查询时间：10299=10秒

方案二基于mybatis-plus，在xml中自定义SQL语句

<!--mapper.xml-->    
<select id = "findAll" fetchSize="10000" resultType = "com.softscenene.server.drugPurchase.domain.hospLedger.dailyAmt.dao.DailyAmt">
        SELECT
            check_date,hosp_id,yesterday_amt,recharge_amt,payment_amt
        from
            hosp_daily_amt
    </select>

@Mapper//mapper.java
public interface DailyAmtMapper extends BaseMapper<DailyAmt> {
    List<DailyAmt> findAll();
}

//DailyAmtService.java    
public void findAll(){
        long startDateTime=System.currentTimeMillis();
        List<DailyAmt> list=dailyAmtMapper.findAll();;
        long endDateTIme=System.currentTimeMillis();
        log.info("【查询日金额表所有数据】消耗时间:{},list长度:{}",(endDateTIme-startDateTime),list.size());
    }

执行以上代码耗时9989毫秒=9.9秒

方案三：使用JDBC自定义查询

import lombok.SneakyThrows;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Component;
import javax.annotation.Resource;
import java.sql.*;
import static com.softscenene.server.drugPurchase.config.jdbc.PropertiesInfo.DBINFO_MYSQL;

/**
 * @日期: 2022/5/24       @作者: 离染
 * @描述: 使用jdbc查询，与在xml中，自定义sql的主要区别：fetchSize相同的情况下,
 * xml根据列名解析数据库返回的数据太耗时，自己写的JDBC则根据列索引直接取，数据越多，收益越大，
 * 特别是查询百万条数据时，jdbc效率是xml自定义sql的数十倍，xml自定义sql效率又是原生的数十倍
 */
@Slf4j
@Component
public class JDBCConnection {
    private Connection conn=null;
    private Statement stmt=null;
    private ResultSet rs=null;

    private final int FETCH_SIZE=10000;

    @Resource
    @Qualifier("mysql")
    private DBInfo dbInfoMysql;
    @Resource
    @Qualifier("oracle")
    private DBInfo dBInfoOracle;

     /** @日期: 2022/5/25       @作者: 离染
      *  @描述:  连接数据库并执行SQL语句
      *  */
    @SneakyThrows
    public ResultSet connection(String sql,String dbName){
        log.info("自定义JDBC——连接数据库——连接参数:{}",dbName);
        DBInfo dbInfo=DBINFO_MYSQL.equals(dbName)?dbInfoMysql:dBInfoOracle;
        if(dbInfo==null){
            log.warn("JDBC连接数据库——获取配置信息失败，数据源名称不存在.dbinfo:{}",dbInfo);
            return null;
        }
        //注册驱动
        DriverManager.registerDriver((Driver) Class.forName(dbInfo.getDriverClassName()).newInstance());
        //获取连接
        conn= DriverManager.getConnection(dbInfo.getUrl(),dbInfo.getUsername(),dbInfo.getPassword());
        //获取数据库操作对象
        stmt=conn.createStatement();
        stmt.setFetchSize(FETCH_SIZE);
        rs=stmt.executeQuery(sql);//执行给定SQL语句，该语句返回单个ResultSet对象
        return rs;
    }

    @SneakyThrows
    public void close() {
        rs.close();
        stmt.close();
        conn.close();
    }
}

 @Test
    void test() throws SQLException {
        long startDateTime=System.currentTimeMillis();
        ArrayList<DailyAmt> arrayList=new ArrayList<>();
        String sql="SELECT check_date,hosp_id,yesterday_amt,recharge_amt,payment_amt from hosp_daily_amt";
        ResultSet resultSet=jdbcConnection.connection(sql,DBINFO_MYSQL);
        while (resultSet.next()){
            DailyAmt dailyAmt=new DailyAmt();
            dailyAmt.setCheckDate(resultSet.getString(1));
            dailyAmt.setHospId(resultSet.getString(2));
            dailyAmt.setYesterdayAmt(new BigDecimal(resultSet.getString(3)));
            dailyAmt.setRechargeAmt(new BigDecimal(resultSet.getString(4)));
            dailyAmt.setPaymentAmt(new BigDecimal(resultSet.getString(5)));
            arrayList.add(dailyAmt);
        }
        long endDateTIme=System.currentTimeMillis();
        log.info("【查询日金额表所有数据】消耗时间:{},list长度:{}",(endDateTIme-startDateTime),arrayList.size());
    }

自定义JDBC，耗时6秒?

?另外，连接参数也是影响性能的因素，附上mysql连接URL:

jdbc:mysql://8.0.0.158:3306/drug?serverTimezone=GMT%2B8&useUnicode=true&characterEncoding=utf-8&useSSL=false&autoReconnect=true&rewriteBatchedStatements=true

总结：影响性能的主要因素主要有2个，fetchsize大小，以及其解析字段所消耗时间，字段越多，解析耗时越长。?