Sql»ù±¾Óï¾äµÄѧϰ

--²éѯÿ¸öÈ˶©·¹µÄ´ÎÊý
select  username as ÐÕÃû, count(*) as ´ÎÊý from orderitems  group by UserName having count(*)=1
order by ÐÕÃû desc
select distinct username as δע²áÐÕÃû from orderitems
where username not in (select [Name] from Person)
select distinct username as ÒÑ×¢²áÐÕÃû from orderitems where username
in (select [Name] from Person)
--Ë÷ÒýΪ31-40µÄÊý¾Ý
select top 10 * from orderitems where ID not in (select top 30 ID from orderitems)
--¸´ÖÆÊý¾Ý
insert into  distinctselect(UserName,State,OrderTime) select UserName,State,OrderTime from orderitems
--È¥³ýËùÓÐÖظ´µÄ¼Ç¼(ÍêÈ«Öظ´)
select distinct UserName ,ID, State,OrderTime into #Table1 from [distinctselect]
delete from [distinctselect]
insert into [distinctselect](UserName,State,OrderTime) select UserName,State,OrderTime from #Table1
drop table #Table1
--ɾ³ýijÁÐÖظ´µÄ¼Ç¼
delete   t  
  from   [distinctselect]   t  
  where   exists   (  
  select   1   from   [distinctselect]  where   username=t.username   and   id<t.id) 
select * from [distinctselect] order by username
delete from [distinctselect]