group by分組查詢小結

1.按某一字段分組后查詢某一條件下的所有數據：如下面的按照ReservePhone:手機號分組后，再查詢是特定的手機號的所有數據

select ID , GroupCode,HotelCode,AccountNo,ReservePhone,ReserveName,RoomNo,RoomType from Res_RoomResource 
where ID in (select (ID) from Res_RoomResource where GroupCode='0001' and hotelcode='021002' group by  ReservePhone,ID) 
and ReservePhone='18537*****';

下面這樣查的話只能查詢到一條記錄
select ID , GroupCode,HotelCode,AccountNo,ReservePhone,ReserveName,RoomNo,RoomType from Res_RoomResource 
where ID in (select min(ID) from Res_RoomResource where GroupCode='0001' and hotelcode='021002' group by  ReservePhone,ID) 
and ReservePhone='18537693630';--min(ID) 或者Max(ID)

補充：

1.對於表TA中存在主鍵id,所以可利用主鍵id來查詢：

select ID , CODE , VALUE ,  DESC  , DATE form TA where ID in (select min(ID) from TA group by CODE , VALUE) ;

2.對於表TB中,表不存在主鍵，則查詢方式為：

select min(ID) ID, CODE , VALUE ,  min(DESC) DESC ,min( DATE) DATE  from TA group by CODE , VALUE ;

總結：

方式1一般都適用 於單表的查詢，因為一般建表的時候都會建主鍵;對於視圖，聯查的時候，方式一可能就不合適了，就可以用方式2