调用标量值函数时，ExecuteScalar始终返回null [英] ExecuteScalar always returns null when calling a scalar-valued function

问题描述

为什么返回空值？

//seedDate is set to DateTime.Now; con is initialized and open. Not a problem with that
using (SqlCommand command = new SqlCommand("fn_last_business_date", con))
{
       command.CommandType = CommandType.StoredProcedure;
       command.Parameters.AddWithValue("@seed_date", seedDate);//@seed_date is the param name
       object res = command.ExecuteScalar(); //res is always null 
}

但是当我直接在数据库中以

But when I call this directly in the DB as follows:

select dbo.fn_last_business_date('8/3/2011 3:01:21 PM') 
returns '2011-08-03 15:01:21.000' 

这是我希望看到的结果我从代码中调用

which is the result I expect to see when I call it from code

为什么，为什么，为什么？

Why, why, why?

推荐答案

尝试：

using (SqlCommand command = new SqlCommand("select dbo.fn_last_business_date(@seed_date)", con))
{
       command.CommandType = CommandType.Text;
       command.Parameters.AddWithValue("@seed_date", seedDate);//@seed_date is the param name
       object res = command.ExecuteScalar(); //res is always null 
}

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