算不了。通过SQL查询从db访问？ [英] Count no. Of visit from db by SQL query?

问题描述

我想要完全没有。访问过的患者。

i将以下代码用c＃作为：

 OleDbCommand vst = new OleDbCommand（select_get（*）from old_patient where Contact_no = @Contact_no GROUP BY Contact_no，cn）; 
 vst.Parameters.Add（new OleDbParameter（@ Contact_no，txtsno.Text））; 
 
 //将值存储在rec变量中。 
 int rec =（int）vst.ExecuteNonQuery（）; 
 lbldtr.Text = rec.ToString（）; 

txtsno是文本框;

lbldtr是我希望显示或打印答案的标签。


$ t $ bxtsno文本框中的b $ b有联系号码。所以，我希望得到特别的联系。访问。



提前谢谢



我尝试了什么：

 OleDbCommand vst = new OleDbCommand（从old_patient中选择count（*），其中Contact_no = @ Contact_no GROUP BY Contact_no，cn）; 
 vst.Parameters.Add（new OleDbParameter（@ Contact_no，txtsno.Text））; 
 
 //将值存储在rec变量中。 
 int rec =（int）vst.ExecuteNonQuery（）; 
 lbldtr.Text = rec.ToString（）; 

解决方案

您可能忘记在问题中写下您的问题了。

查看你的代码，它有以下错误

1.查询似乎不正确

  select  count（*）来自 old_patient 其中 Contact_no = @Contact_no  GROUP   BY  Contact_no 

应该be-

 选择 count（*）来自 old_patient 其中 Contact_no = @ Contact_no 

2.您应该使用ExecuteScalar而不是ExecuteNonQuery

  int  rec =（ int ）vst.ExecuteNonQuery（ ）; 

它应该是 -

  int  rec =（< span class =code-keyword> int ）vst.ExecuteScalar（）; 

这是详细阅读的详细文章 -

ExecuteReader ExecuteScalar和ExecuteNonQuery之间的区别 [ ^ ]



希望，它有帮助:)

如果您发现更多困难，请告诉我。

使用 ExecuteScalar [ ^ ]

ExecuteNonQuery 将返回受影响的行数，而不是您想要返回的实际值。

  int  rec =（ INT ）vst.ExecuteScalar（）; 

i want to total no. of visited patient.
i make following code in c# as:

OleDbCommand vst = new OleDbCommand("select count(*) from old_patient where Contact_no=@Contact_no GROUP BY Contact_no", cn);
                        vst.Parameters.Add(new OleDbParameter("@Contact_no", txtsno.Text));

                        //  store value in rec variable.
                        int rec = (int)vst.ExecuteNonQuery();
                        lbldtr.Text = rec.ToString();

txtsno is textbox;
lbldtr is label where i want to show or print answer.

in txtsno textbox have contact no. so , i want to get particular contact no. visit.

thank u in advance

What I have tried:

OleDbCommand vst = new OleDbCommand("select count(*) from old_patient where Contact_no=@Contact_no GROUP BY Contact_no", cn);
                        vst.Parameters.Add(new OleDbParameter("@Contact_no", txtsno.Text));

                        //  store value in rec variable.
                        int rec = (int)vst.ExecuteNonQuery();
                        lbldtr.Text = rec.ToString();

解决方案

You probably have forgotten to write your problem in the question.
Looking at your code, it has following mistakes
1. Query seems to be incorrect

select count(*) from old_patient where Contact_no=@Contact_no GROUP BY Contact_no

It should be-

select count(*) from old_patient where Contact_no=@Contact_no

2. You should use ExecuteScalar instead of ExecuteNonQuery

int rec = (int)vst.ExecuteNonQuery();

it should be-

int rec = (int)vst.ExecuteScalar();

Here is a detailed article for detailed reading-
Difference between ExecuteReader ExecuteScalar and ExecuteNonQuery[^]

Hope, it helps :)
If you find further difficulties, please let me know.

use ExecuteScalar [^]
ExecuteNonQuery will return the number of rows affected, not the actual value which you want to return.

int rec = (int)vst.ExecuteScalar();

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