12、springboot-数据库数据提取及详细处理

疫情大数据平台，后台首要的任务是从各种渠道获得数据及对获取后的数据进行处理，本篇主要是记录各类历史数据从数据库中取出，并进行详细处理的过程

主要使用MybatisPlus进行复杂查找

MybatisPlus进行简单查找时较为方便，但进行复杂查找时，需要注意的地方有很多，也比较麻烦

例如

sql语句：sql = "SELECT max(confirm),cast(sum(confirm_add) as signed),date_format(date,'%Y-%m') " \
          "FROM epidemicplatform.province_history " \
          "where province={} " \
          "GROUP BY DATE_FORMAT(date, '%Y-%m');"

查询语句中不能出现下划线，及较低版本的sql中，出现在select中的字段也必须出现在group by中，否则会报错

 QueryWrapper<Province_history> queryWrapper1 = new QueryWrapper<>();
        queryWrapper1.eq("province",region);
        queryWrapper1.groupBy("DATE_FORMAT(date, '%Y-%m')").select("max(confirm) as maxconfirm","DATE_FORMAT(date, '%Y-%m') as d","sum(confirm_add) as sumconfirmadd");
               

部分提取代码

 QueryWrapper<Province_history1> queryWrapper1 = new QueryWrapper<>();
        queryWrapper1.eq("province", region);
        queryWrapper1.ge("date","2022-04-01");
        queryWrapper1.groupBy("DATE_FORMAT(date, '%Y-%m-%d')").select("DATE_FORMAT(date, '%Y-%m-%d') as date1","heal_add as sumhealadd","dead_add as sumdeadadd","confirm_add as sumconfirmadd");
        List<Province_history1> history = province_historyMapper1.selectList(queryWrapper1);

 QueryWrapper<Province_history1> queryWrapper3 = new QueryWrapper<>();
            queryWrapper3.eq("province", region);
            queryWrapper3.ge("date", "2022-05-01");
            queryWrapper3.groupBy("date").select("date");
            List<Province_history1> daten = province_historyMapperX.selectList(queryWrapper3);

 QueryWrapper<Province_history1> queryWrapper1 = new QueryWrapper<>();
            queryWrapper1.eq("province", region);
            queryWrapper1.ge("date", "2022-05-01");
            queryWrapper1.select("date as date1", "confirm as sumconfirmadd");
            List<Province_history1> history = province_historyMapperX.selectList(queryWrapper1);

            QueryWrapper<City_history1> queryWrapper2 = new QueryWrapper<>();
            queryWrapper2.eq("province_name", region);
            queryWrapper2.ge("date", "2022-05-01");
            queryWrapper2.groupBy("city_name").select("city_name");
            List<City_history1> cityn = city_historyMapper1.selectList(queryWrapper2);

整体来说，数据提取是较为简单的，较难的是数据处理成需要的样子再传给前端，采用的是手动构造的方法，让部分数据拼接。
其中需要注意的是复杂数组的取数通用性问题，以及部分数据提取失效的问题，取数的是很好由于一些原因，能正常获得长度，但取出的数据全部为null，只能转为其他列名取出，此时取数通用性问题就较为繁琐，因为虽然数据的排序整体有一定的顺序，但是几乎不可能符合前端的格式要求，要根据整体的逻辑进行复制的数据提取

部分代码，由于过于繁琐，就只展示少量处理过程

  for (int i = 0; i < t_number; i = i + date_number) {
                if (i != t_number - date_number)
                    fin = fin + " \"" + history.get(i).getCity() + "\"" + ",";
                else
                    fin = fin + " \"" + history.get(i).getCity() + "\"" + "]";
            } 
            for (int i = 0; i < date_number; i++) {
                if (i != date_number - 1)
                    fin = fin + " \"" + history.get(i).getDate1() + "\"" + ",";
                else
                    fin = fin + " \"" + history.get(i).getDate1() + "\"" + "]";
            }
            int q = 0;
            for (int i = 0; i < t_number; i = i + date_number) {

                fin = fin + "\n" +
                        "   [";
                for (int x = 0; x < date_number; x++) {
                    if (q == t_number) break;
                    if (q % date_number != date_number - 1)
                        fin = fin + " " + history.get(q).getConfirm1() + ",";
                    else
                        fin = fin + " " + history.get(q).getConfirm1() + "]";
                    q++;
                }

                if (i != t_number - date_number)
                    fin = fin + ",";
                else
                    fin = fin + "]";
            }

            for (int i = 0; i < date_number; i++) {
                if (i != date_number - 1)
                    fin = fin + " \"" + history.get(i).getDate1() + "\"" + ",";
                else
                    fin = fin + " \"" + history.get(i).getDate1() + "\"" + "]";
            }
            for (int i = 0; i < date_number; i++) {
                if (i != date_number - 1)
                    fin = fin  + history.get(i).getSumconfirmadd() + ",";
                else
                    fin = fin  + history.get(i).getSumconfirmadd() + "]]";
            }