当没有数据存在时，invalide尝试读取 [英] invalide attempt to read when no data is present

问题描述

我正在验证一个列日期大于或小于今天日期的数据库。



我的代码如下

I am validating database of one column date greater than or lesser than today date.

My code as follows

SQl = "select sp_issu_dt from student_professional 
where stud_id = " + id + " and pm_prof_code = 'medrep'";
      drmedical = SCon.ReadSql(SQl);
if (drmedical.Read()&&  drmedical.HasRows &&(Convert.ToDateTime(drmedical[0]) > Convert.ToDateTime(GetDate)))
                    {
                        med = "himt";
                     }

当我运行上面的代码时显示如下错误



无效尝试阅读当没有数据时。



当我在drmedical [0]中执行时，未检索到值。



请帮我解决我犯的错误。

When i run the above code shows error as follows

Invalid attempt to read when no data is present.

When i execute in drmedical[0] value is not retrieved.

Please help me what is the mistake i made.

推荐答案

你必须打电话给DataReader.Read 首先获取结果：

You have to call DataReader.Read first to fetch the result:

string SQl = "select sp_issu_dt from student_professional
where stud_id = " + id + " and pm_prof_code = 'medrep';
SqlCommand cmd = new SqlCommand(SQL);
SqlDataReader dr = cmd.ExecuteReader();

//drmedical = SCon.ReadSql(SQl);
if (dr.Read() &&  dr.HasRows &&(Convert.ToDateTime(drmedical[0]) 
// ... and so long

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