C#on UPDATE语句中的SQL参数问题

我正在尝试更新数据。每当我使用参数化查询时，它都会给出在命令执行过程中遇到的错误

致命错误

这是我的密码：

public void updateAccount(Int32 cashierid, string cashieruser, string isadmin, string cashierfname, string cashiermname, string cashierlname, string cashierpass)
{
    con.ConnectionString = conString;     
    String sql = "UPDATE cashieraccount SET cashieruser = ?cashieruser, cashierpass = ?cashierpass, isadmin = ?isadmin, cashierfname = ?cashierfname, cashiermname = ?cashiermname, cashierlname = ?cashierlname";
    sql += "WHERE cashierid = ?cashierid";
    try
    {
        con.Open();
        MySqlCommand cmd = new MySqlCommand(sql, con);
        cmd.Parameters.AddWithValue("?cashieruser", cashieruser);
        cmd.Parameters.AddWithValue("?cashierpass", cashierpass);
        cmd.Parameters.AddWithValue("?isadmin", isadmin);
        cmd.Parameters.AddWithValue("?cashierfname", cashierfname);
        cmd.Parameters.AddWithValue("?cashiermname", cashiermname);
        cmd.Parameters.AddWithValue("?cashierlname", cashierlname);
        cmd.Parameters.AddWithValue("?cashierid", cashierid);
        cmd.ExecuteNonQuery(); **//Fatar Error Encountered during command execution**
    }
    finally
    {
        con.Close();
    }
}

有人有什么建议吗？
我在您的参数后面的
where
子句之前缺少一个空格：

String sql = "UPDATE cashieraccount SET cashieruser = ?cashieruser, cashierpass = ?cashierpass, isadmin = ?isadmin, cashierfname = ?cashierfname, cashiermname = ?cashiermname, cashierlname = ?cashierlname";
sql += " WHERE cashierid = ?cashierid";
// here ^ 

在
where
子句之前，您的参数后面缺少一个空格：

String sql = "UPDATE cashieraccount SET cashieruser = ?cashieruser, cashierpass = ?cashierpass, isadmin = ?isadmin, cashierfname = ?cashierfname, cashiermname = ?cashiermname, cashierlname = ?cashierlname";
sql += " WHERE cashierid = ?cashierid";
// here ^