当我从Web应用程序执行此sql语句时，它提供了一些错误 [英] when i executing this sql statement from web application it is providing some error

问题描述

select sum(amountpaid) from tbl_payments where uid=29

它越来越空

如何检查状况
我正在尝试这样

it is getting null

how to check the condition
i am trying like this

if(cmd.executescaler()==null)

但它正在生成

无效的强制dbnull不能强制转换为其他类型.

but it is generating the

invalid cast dbnull cannot be cast to other types.

SqlCommand cmd = new SqlCommand("select sum(isnull(amountpaid,0)) from tbl_payments tbl_payments where uid=" + Label2.Text, con);
                amount = Convert.ToInt64(cmd.ExecuteScalar());
                if(amount!=0)
                 {

当标量和函数恢复为null时，它会得到无法将dbnull转换为其他类型的错误

when the scalar sum funtion returing null.it is getting the error like cannot cast from dbnull to other types

推荐答案

，您可以像这样尝试

you can try like this

select isnull(sum(isnull(amountpaid,0)),0) from tbl_payments where uid=29

您可以将此cmd execute分配给任何整数变量，并检查像这样的条件.

Hi,
you can assign this cmd execute to any integer variable,and check that condition like this.

int result = Convert.ToInt32(cmd.ExecuteScalar());
if(result==0)
{

}

您可以遵循以下代码:

Hi,

You can following code:

string ConString = ConfigurationManager.ConnectionStrings["ConString"].ConnectionString;
SqlConnection con = new SqlConnection(ConString);
string CmdString = "select sum(isnull(amountpaid,0)) from tbl_payments where uid=@UID";
SqlCommand cmd = new SqlCommand(CmdString, con);
cmd.Parameters.AddWithValue("@UID", 5734999994);
con.Open();
double AmountPaid;
if (cmd.ExecuteScalar() != null)
{
    AmountPaid = Convert.ToDouble(cmd.ExecuteScalar());
}
con.Close();

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