＆＃34;必须声明标量变量＆＃34;错误

Question

  

必须声明标量变量“@Id”

SqlConnection con = new SqlConnection(@"connectionstring");
con.Open();
SqlCommand cmd = new SqlCommand();
cmd.Connection = con;
cmd.CommandText = ("SELECT Goal from Planning WHERE Id = @Id");
int goal = (int)cmd.ExecuteScalar();

有人能帮助我吗？

Answer 1

因为您在Id中声明了SqlCommand参数，但未添加任何值。

当你在CommandText财产中分配文字时，你不需要使用()。

cmd.CommandText = "SELECT Goal from Planning WHERE Id = @Id";
cmd.Parameters.AddWithValue("@Id", YourIdValue);
int goal = (int)cmd.ExecuteScalar();

还可以使用using statement来处置您的SqlConnection和SqlCommand。

这是一个完整的例子;

using(SqlConnection con = new SqlConnection(connString))
using(SqlCommand cmd = new SqlCommand())
{
     cmd.Connection = con;
     cmd.CommandText = "SELECT Goal from Planning WHERE Id = @Id";
     cmd.Parameters.AddWithValue("@Id", YourIdValue);
     try
     {
         conn.Open();
         int goal = (int)cmd.ExecuteScalar();
     }
     catch (Exception ex)
     {
         Console.WriteLine(ex.Message);
     }
}

Answer 2

您应该为参数

指定一个值

cmd.Parameters.AddWithValue("@Id", value);