指定的转换使用C＃有效的错误 [英] Specified cast is not valid error using C#

问题描述

我想储存在C＃中的变量的SELECT语句的结果，但得到这个错误

  

规定的强制转换无效

当我运行它。我不知道如何解决它，请帮助

  SqlConnection的CON1 =新的SqlConnection（ConfigurationManager.ConnectionStrings [MyConnectionString]的ConnectionString）;        CMD1的SqlCommand =新的SqlCommand（SELECT CAST（圆（SUM（CAST（AvgNumbers为数字（12,2））），2）十进制（12,2））AS [平均天数]从MainTable，CON1）;        cmd1.Connection = CON1;
        con1.Open（）;
        INT32结果=（Int32）已cmd1.ExecuteScalar（）;
        con1.Close（）;
 

解决方案

cmd1.ExecuteScalar（）没有返回一个整数盒装。其分配给一个对象，看看它在调试器，看看它到底是什么。

我猜这将是返回一个小数或双，而你需要做的：

 的Int32结果=（Int32）已（双）cmd1.ExecuteScalar（）;
 

或者

 的Int32结果=（Int32）已（十进制）cmd1.ExecuteScalar（）;
 

要保持十进制值，只是这样做：

 十进制结果=（十进制）cmd1.ExecuteScalar（）;
 

如果你需要，你可以十进制转换为双：

 双重结果=（双）（十进制）cmd1.ExectuteScalar（）;
 

I am trying to store a select statement result in C# variable but getting this error

"Specified cast is not valid"

when i run it. I am not sure how to resolve it please help

SqlConnection con1 = new SqlConnection(ConfigurationManager.ConnectionStrings["MyConnectionString"].ConnectionString);

        SqlCommand cmd1 = new SqlCommand("select cast(round(sum(CAST(AvgNumbers AS numeric(12,2))),2) as decimal(12,2)) AS [Average Days] from MainTable ", con1);

        cmd1.Connection = con1;
        con1.Open();
        Int32 result = (Int32)cmd1.ExecuteScalar();
        con1.Close();

解决方案

cmd1.ExecuteScalar() is not returning a boxed integer. Assign it to an object and look at it in the debugger to see what it really is.

I'm guessing it's going to be returning a Decimal or a double, and you need to do:

Int32 result = (Int32)(double)cmd1.ExecuteScalar();

Or:

Int32 result = (Int32)(Decimal)cmd1.ExecuteScalar();

[EDIT in response to a question in commments below]

To keep the decimal value, just do this:

Decimal result = (Decimal) cmd1.ExecuteScalar();

If you needed to, you could cast the decimal to a double:

double result = (double)(Decimal) cmd1.ExectuteScalar();

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