平均值的平均值

Question

我有一个名为ranks的表，它存储1-7值。

r_id | r_userid | r_class | r_showcaseid | r_submitterid

r_class是1-7值，r_showcaseid是给定评级的项目。

以下查询选择用户前5个提交（r_showcaseid）的平均评分。我需要获得行的平均值＆＃39;此查询的值（即平均值的平均值）：

SELECT avg(r_class) FROM ranks WHERE r_submitterid=? GROUP BY r_showcaseid ORDER BY avg(r_class) DESC LIMIT 5

所以，我想要的值是（6 + 5 + 1.5）/3≈4.166......

我试过avg(avg(r_class))，但这给了我一个错误。如何从查询中获取行的avg(r_class)的平均值？

Answer 1

    try 
    {
    // Get Connection
    Connection connection = SQLServer.getSQLServerConnection();

    // Create statement
    Statement statement = connection.createStatement();

    String sql = " select    distinct   PositionTitle, max(NumberOFCount) as  votes From votecount  Group By  PositionTitle order by  votes desc";
    //Execute SQL statement returns a ResultSet object.
    ResultSet rs = statement.executeQuery(sql);
    List<String> position =new ArrayList<>();
    List<String> count =new ArrayList<>();


    int i = 0;
    while(rs.next() && i<6){


         position.add(i, rs.getString(1));
         count.add(i, rs.getString(2));
         i++;
    } 

    rs.close();

    String[] pstn = (String[]) position.toArray(new String[position.size()]);
    String[] cnt = (String[]) count.toArray(new String[count.size()]);


         /* Iterator<String> postn = position.iterator();
         Iterator<String> cnt = count.iterator(); */

        for(int j=0;j<6;j++)
         {

          String sql1 = " Select FirstName from votecount where PositionTitle ='"+pstn[j]+"' and NumberOFCount = '"+cnt[j]+"'";
         ResultSet rs1 = statement.executeQuery(sql1);

             String FirstName = rs1.getString(0);

        %>
        <p align="center"><%=pstn[j] %> : <%=FirstName %>  </p>
        <p></p>

<%      


         }
}
catch (Exception e)
{
    e.printStackTrace (response.getWriter());
}%>

您可以使用外部查询来执行此操作。