c# - sql server strange behavior (query time respond) -

i asked question "timeout expired, optimize query" problem time respond sql server query :

using (sqlconnection sqlconn = new sqlconnection(sqlservermasterconnection)) {   if (sqlconn.state != connectionstate.open) sqlconn.open();   using (sqlcommand cmd = new sqlcommand("select dt.* detailtable dt, billtable bt, packagetable pt                                           pt.id= bt.idpackage , dt.idbill= bt.id                                           ,  pt.codecompany = @codecompany , pt.date between @begin , @end",                                          sqlconn))  {     cmd.parameters.add(new sqlparameter(@begin , begindate));     cmd.parameters.add(new sqlparameter("@end", enddate));     cmd.parameters.add(new sqlparameter("@codecompany", codecompany));     using (dbdatareader reader = cmd.executereader())     {        while (reader.read())        {           //work todo        }     }  } } 

it take 28 sec 20,000 record,

the strange behavior wrote

using (sqlconnection sqlconn = new sqlconnection(sqlservermasterconnection)) {   if (sqlconn.state != connectionstate.open) sqlconn.open();   using (sqlcommand cmd = new sqlcommand("select dt.* detailtable dt, billtable bt, packagetable pt  pt.id= bt.idpackage , dt.idbill= bt.id                                           ,  pt.codecompany = @codecompany , pt.date between '" + begindate + "' , '" + enddate + "'"                                          ,sqlconn))  {     cmd.parameters.add(new sqlparameter("@codecompany", codecompany));     using (dbdatareader reader = cmd.executereader())     {        while (reader.read())        {           //work todo        }     }  } } 

i changed @date sent value without sqlparameter , got result in 0 sec !!

any suggestion result

ps :

• we save date in database string yyyymmdd (pt.date varchar(8))
• begindate , enddate string (20130904)

if query isn't changing in structure , you're executing same parameters perhaps sql server caching results of query, see question similar issue.