sqlserver中用stuff实现类似wm_concat功能，将某一列的多行值拼成一个字符串

string deviceCode=dt.Rows[i]["code"].ToString();
string sql_logtime = @"select  stuff((
select ','+CONVERT(Nvarchar,l2.logtime, 20)  from logs_signIn l2 where CONVERT(Nvarchar,l2.logtime, 23)='" + DateTime.Now.ToString("yyyy-MM-dd") + @"'  
order by l2.logtime desc 
FOR XML PATH(''))
,1,1,'') logtimes ";
object obj = DbHelperSQL.GetSingle(sql_logtime);