sql 错误 "Input string was not in a correct format"

Question

我无法从我的 sql 数据库中获取 int 值：

if(Convert.ToDouble(dbh.getInfo("firstTime", username))==1)

我也试过了：

if((int)dbh.getInfo("firstTime", username)==1)

这是 getInfo 函数：

public object getInfo(string infoReq, string username)
        {
            string query = "select (@infoReq) from AccountDB where username like @username";
            try
            {
                using (SqlConnection con = new SqlConnection(connectionString))
                {
                    SqlCommand cmd = new SqlCommand(query, con);
                    cmd.Parameters.AddWithValue("@infoReq", infoReq);
                    cmd.Parameters.AddWithValue("@username", username);
                    con.Open();
                    return cmd.ExecuteScalar();
                }
            }
            catch (Exception e){

            }
            return MessageBox.Show("Please check your fields");
        }

dbh 是一个 DBHandler 类型，这当然是该函数的来源

在sql数据库中，这个@infoReq的DataType对于这件事有点（在sql中：[firstTime] BIT NOT NULL）

我的代码有什么问题？

Answer 1

试试这个：

public object getInfo(string infoReq, string username)
{
    string query = "select @infoReq from AccountDB where username like '%@username%'";
    try
    {
        using (SqlConnection con = new SqlConnection(connectionString))
        {
            SqlCommand cmd = new SqlCommand(query, con);
            cmd.Parameters.AddWithValue("@infoReq", infoReq);
            cmd.Parameters.AddWithValue("@username", username);
            con.Open();
            return cmd.ExecuteScalar();
        }
    }
    catch (Exception e){

    }
    return MessageBox.Show("Please check your fields");
}

sql 错误 "Input string was not in a correct format"

Error "Input string was not in a correct format" with sql

c#

sql-server

ssms