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问题:
I have two tables, named t_master and t_detail.
The data in the t_detail table corresponds to a record on the master table.
Data of t_master
ID Brand 1 Toyota 2 Honda
Data for the t_detail
DetID ParentID Model 1 1 Corolla 2009 2 1 Corolla 2010 3 1 Corolla 2011 4 2 Civic 2004 5 2 Civic 2006
Now, I want to make a query that should select all rows in the master table and at the same time, select the detail which has the latest ID (max), i.e.
ID Brand DetID ParentID Model 1 Toyota 3 1 Corolla 2011 2 Honda 5 2 Civic 2006
Appreciate your help. Thanks.
回答1:
Use:
SELECT m.id, m.brand, x.detid, x.parentid, x.model FROM T_MASTER m JOIN T_DETAIL x ON x.parentid = m.id JOIN (SELECT d.parentid, MAX(d.detid) AS max_detid FROM T_DETAIL d GROUP BY d.parentid) y ON y.max_detid = x.detid AND y.parentid = x.parentid
回答2:
SELECT Make.ID, Make.Brand, Model.DetID, Model.Model FROM t_master Make INNER JOIN t_detail Model ON Make.ID = Model.ParentID WHERE DetID = ( SELECT MAX(DetID) From t_detail WHERE ParentID = Make.ID )
回答3:
Please note that if you have more rows in Master Table and there are no rows in Detail Table that fits , but you still want to show ALL master table rows then you should initiate the below :
( Please note that you have to add 2 more rows to the master table) for example :
ID Brand 1 Toyota 2 Honda 3 Porsche 4. Volvo In order to get the following result : ID BRAND DETID PARENTID MODEL 1 Toyota 3 1 Corolla 2011 2 Honda 5 2 Civic 2006 4 Volvo - - - 3 Porcshe - - -
Then do the following select (a bit different syntax for the ease of Oracle Users) :
SELECT m.id, m.brand, x.detid, x.parentid, x.model FROM T_MASTER m, T_DETAIL x, (SELECT m.id,NVL(MAX(d.detid),1) AS max_detid FROM T_DETAIL d, T_MASTER m WHERE m.id = d.parentid (+) GROUP BY m.id) y WHERE m.id = x.parentid (+) AND y.max_detid = NVL(x.detid,1) AND y.id = m.id
