按日期添加生成单号

 public string GetNext挂号代码(string 登记日期)
        {
            string strReturn = "";
            StringBuilder strSql = new StringBuilder();
            strSql.Append(" select MAX(Regid) as maxgh");
            strSql.Append(" from Us_ghxx ");
            strSql.Append("   where  (select CONVERT(varchar(12) ,Ghrq, 112 ) )='" + 登记日期 + "' ");
            DataSet ds = DbHelperSQL.Query(strSql.ToString());

            int int挂号代码 = 0;
            if (ds.Tables[0].Rows[0]["maxgh"].ToString().Trim() == "")
            {
                strReturn = 登记日期 + "00001";
            }
            else
            {

                string strTmp = ds.Tables[0].Rows[0]["maxgh"].ToString();
                int挂号代码 = int.Parse(strTmp.Substring(8, 5));

                int挂号代码 = int挂号代码 + 1;

                string str挂号代码 = int挂号代码.ToString().Trim();
                if (str挂号代码.Length == 1)
                {
                    str挂号代码 = "0000" + str挂号代码;
                }
                else if (str挂号代码.Length == 2)
                {
                    str挂号代码 = "000" + str挂号代码;
                }
                else if (str挂号代码.Length == 3)
                {
                    str挂号代码 = "00" + str挂号代码;
                }
                else if (str挂号代码.Length == 4)
                {
                    str挂号代码 = "0" + str挂号代码;
                }
                strReturn = 登记日期 + str挂号代码;
            }

            return strReturn;
        }