偶然发现的一个有点奇怪的SQL语句问题

在写一个计算贷款利息的语句时发现的。strsql="UPDATE plus_bank SET savemoney=savemoney（1+@lixi）-@qukuan,savedate=@savedate where userid=" + userid;
这句在ExecuteNonQuery时出错，报找不到函数savemoney,而下面的则可以，觉得有点奇怪，难道SQL语句还有这种局限性。
strsql="UPDATE plus_bank SET savemoney=savemoney+savemoney*@lixi-@qukuan,savedate=@savedate where userid=" + userid;
     SqlCommand cmd3 = new SqlCommand(strsql,myConn);
     cmd3.Parameters.Add("@lixi",SqlDbType.Float,4).Value = rate*(DateTime.Now.Year-mysavedate.Year+(DateTime.Now.Month-mysavedate.Month));
     cmd3.Parameters.Add("@qukuan",SqlDbType.Int,4).Value = myqukuan;
     cmd3.Parameters.Add("@savedate",SqlDbType.DateTime,4).Value = DateTime.Now;
     try
     {
      dr.Close();
      cmd3.ExecuteNonQuery();
     }
     catch(Exception Ex)
     {
      Response.Write("Q异常捕获！"+Ex);
      Response.End();
     }