问题描述

怎么根据年份统计数据库中各列的总值

数据库里面只有时间字段（包括年月日）资产名称，资产数量，资产金额，学校名称，怎样
按年度统计统计每年学校的资产总数，总金额，会的能提点下么？，求指点，能告诉大概
的方法，思路都好，在线等，谢谢 （java)

解决方案

 class Record{    private String dateStr = """";    private String schoolName = """";    private int money = 0;    public Record(String dateStrString schoolNameint money){        this.dateStr = dateStr;        this.schoolName = schoolName;        this.money = money;    }    public String getYear() {        return dateStr.split(""-"")[0];    }    public String getSchoolName() {        return schoolName;    }    public int getMoney() {        return money;    }}public class Test {     public List<Record> init(){        List<Record> list = new ArrayList();        list.add(new Record(""2015-01-01""学校A""200));        list.add(new Record(""2015-02-01""学校A""300));        list.add(new Record(""2015-03-01""学校A""400));        list.add(new Record(""2015-01-01""学校B""200));        list.add(new Record(""2015-01-01""学校B""600));        list.add(new Record(""2015-02-01""学校B""800));        return list;    }    public HashMap<StringHashMap<StringInteger>> tongJi(List<Record> list){        HashMap<StringHashMap<StringInteger>> rstMap = new HashMap();        for(int i=0;i<list.size();i++){            Record rd = list.get(i);            if(rstMap.get(rd.getYear())==null){                rstMap.put(rd.getYear()new HashMap());                             }            HashMap<StringInteger> schoolMap= rstMap.get(rd.getYear());            if(schoolMap.get(rd.getSchoolName())==null){                schoolMap.put(rd.getSchoolName()0);                  }            Integer value = schoolMap.get(rd.getSchoolName());            value = value + rd.getMoney();            schoolMap.put(rd.getSchoolName()value);              }        return rstMap;    }    public void print(HashMap<StringHashMap<StringInteger>> rstMap){        Iterator  iter1 = rstMap.keySet().iterator();        while(iter1.hasNext()){            String year = (String)iter1.next();            HashMap<StringInteger> schoolMap= rstMap.get(year);            Iterator iter2 = schoolMap.keySet().iterator();            while(iter2.hasNext()){                String schoolName = (String)iter2.next();                int value = schoolMap.get(schoolName);                System.out.println(""year=""+year+""school=""+schoolName + ""金额=""+value);            }        }    }    /**     * @param args     */    public static void main(String[] args) {         Test t = new  Test();         List<Record> list = t.init();         HashMap map = t.tongJi(list);//统计         t.print(map);    }}

解决方案二：

 select sum(资产金额) from 表 group by 学校名称年份(日期取年，数据库都有对应的函数)

解决方案三：
sql中的sum(字段名)就能实现这个功能