Question

我创建了功能分析学生结果表。目标是：找到按内容类型分组的最高平均结果。例如：

S_Id      ContentType      Result
1              T             50
1              V             70
1              G             30
1              G             40
1              V             60

我需要的输出是V，因为V的平均值是最高的。

这是我的代码，但它没有显示正确的结果：我的输出显示表格中的第五行。

public string analyzeResultTable(string studentId)
{
    string connStr = System.Configuration.ConfigurationManager.ConnectionStrings["AHSConnection"].ToString();
    DataSet ds = new DataSet();
    DataSet dsAns = new DataSet();
    string BestPrefrence = "";
    using (MySqlConnection conn = new MySqlConnection(connStr))
    {
        conn.Open();
            MySqlCommand cmd2 =
            new MySqlCommand(
                "Select ContentType, MAX(avgContent) from (select ContentType, AVG(result) as avgContent from dopractice where S_Id='" +
                    studentId + "' GROUP BY ContentType) AS T", conn);
            MySqlDataAdapter da = new MySqlDataAdapter(cmd2);
            da.Fill(ds);
            conn.Close();
    }

    if (ds.Tables[0].Rows.Count > 0)
    {
        BestPrefrence = ds.Tables[0].Rows[0]["ContentType"].ToString();
    }
    return BestPrefrence;
}

Answer 1

这将为您提供每个ContentType的平均结果

select ContentType, AVG(result) as avgContent from dopractice where S_Id='" + studentId + "' GROUP BY ContentType order by AVG(result) desc limit 1;

添加订单后，您将得到您想要的内容

Answer 2

您的SQL查询不正确。它可以是下面的东西。

<强>代码

MySqlCommand cmd2 = new MySqlCommand("select ContentType, AVG(Result) as AvgContent 
                         from dopractice 
                         where S_Id='" + studentId + "' 
                         group by ContentType order by 2 desc limit 1;", conn);

我强烈建议您使用参数化查询来避免sql注入。

<强>代码

MySqlCommand cmd2 = new MySqlCommand("select ContentType, AVG(Result) as AvgContent 
                         from dopractice 
                         where S_Id= @S_Id
                         group by ContentType order by 2 desc limit 1;", conn);
cmd2.Parameters.AddWithValue("@S_Id", studentId);

C＃：Select语句没有出现正确的结果

2 个答案: