调用标量值函数时,ExecuteScalar始终返回null

Question

为什么这会返回null？

//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DB中调用它时如下:

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

当我从代码中调用它时,我希望看到的结果

为什么,为什么,为什么？

Answer 1

为什么每个人都坚持select语法？

using (System.Data.SqlClient.SqlCommand cmd = new System.Data.SqlClient.SqlCommand("calendar.CropTime", c))
{
    cmd.CommandType = CommandType.StoredProcedure;
    cmd.Parameters.Add("@RETURN_VALUE", SqlDbType.DateTime).Direction = ParameterDirection.ReturnValue;
    cmd.Parameters.AddWithValue("@d", DateTime.Now);

    cmd.ExecuteNonQuery();

    textBox1.Text = cmd.Parameters["@RETURN_VALUE"].Value.ToString();

}

Answer 2

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 
}