select * from (select distinct id, Row_Number() Over(order by Creattime desc) As rownum, Creattime from ActivityInfo) as d where rownum between 21 And 30 order by Creattime desc
string SQL1="select HelpId from (select distinct HelpId, Row_Number() Over(order by Creattime desc) As rownum, Creattime from HelpAnswer) as d where rownum between ("+pageIndex+"-1)*15+1 And "+pageIndex+"*15 order by Creattime desc";