Question

    ___WORKER_ID___|_______OCCUR________
          20       |         1
          20       |         2
          21       |         3
          22       |         5
          20       |         1


    According to this table, I need to know each worker how many occur?
     Such as   Worker_id=20 has occur is 4   
               Worker_id=21 has occur is 8

我可以通过此代码从这个Worker表中获取两个值

         String sql = "SELECT Table.worker_id,Table.occur FROM keyword_pages Table"
            + " WHERE keyword_id=" + PUID;

        conn = getConnection();
        stm = conn.createStatement();
        rs = stm.executeQuery(sql);
        while (rs.next()) {
            int kwd_id = rs.getInt(1);    /**Worker_id is 20,20,21,22,20*/
            int occur = rs.getInt(2);     /**Worker_id is 1,2,3,5,1*/          

        }

如何获得每个工人的发生量？

这是我的编码。我使用hashmap存储每条记录。并将hashmap存储到linklist。但我对获得结果没有任何想法。

  conn = getConnection();
        stm = conn.createStatement();
        rs = stm.executeQuery(sql);
        while (rs.next()) {
            int kwd_id = rs.getInt(1);
            int occur = rs.getInt(2);
            hMap.put(kwd_id, occur);
            listID.add(hMap);
            //System.out.println(kwd_id +"  |  "+ occur);
        }

        for (int i = 0; i < listID.size(); i++) {


        }

Answer 1

String sql = "SELECT T.worker_id, SUM(T.occur) AS osum"
        + " FROM keyword_pages T"
        + " WHERE keyword_id=" + PUID
        + " GROUP BY T.worker_id";

现在rs.getInt(2)或rs.getInt("osum")会给出小组的总和。

Answer 2

Map<Integer,Integer> id2count = new HashMap<>();

while (rs.next()) {
        int kwd_id = rs.getInt(1);    /**Worker_id is 20,20,21,22,20*/
        int occur = rs.getInt(2);     /**Worker_id is 1,2,3,5,1*/          
   Integer count = id2count.get( kwd_id );
   if( count == null ){
       count = Integer.valueOf( 1 );
   } else {
       count += occur;
   }
   id2count.put( kwd_id, count );
}

**后来**

检索和打印累计值的代码：

for( Integer key: id2count.keySet() ){
    System.out.println( key + ": " + id2count.get(key) );
}

如何从特定记录中汇总数据？

2 个答案: