Question

I have two very simple tables in Oracle 9G:

Customer

userid | firstName | lastName | email 
-------+-----------+----------+---------------------
  1      user1       User1      [e-mail]
  2      user2       User2      [e-mail]

Order

orderiD | userId | OrderType | Order_Date | Amount
--------+--------+-----------+------------+-------
1          1          0         12/12/2009    1
2          1          1         13/12/2009    2
3          1          1         14/12/2009    3
4          2          0         12/12/2009    4
5          2          1         16/12/2009    2
6          1          0         14/12/2009    5
7          2          1         17/12/2009    4
8          2          0         10/12/2010    2

I want to select all users which have orders of type 0

select *    
from Customer c 
inner join Order o on c.userid = o.userid 
where o.orderType = '0'

The result is:

orderiD | userId | OrderType | Order_Date | Amount
--------+--------+-----------+------------+--------
1          1          0         12/12/2009    1
4          2          0         12/12/2009    4
6          1          0         14/12/2009    5
8          2          0         10/12/2010    2

Now I need to modify this query to bring only last purchase date for each user id and get the result like this:

orderiD | userId | OrderType | Order_Date | Amount
--------+--------+-----------+------------+--------
6          1          0         14/12/2009    5
8          2          0         10/12/2010    2

How should I modify my query to get this result?

Answer 1

SELECT * 
FROM order o
WHERE o.orderType ='0'
  AND o.order_date = 
      ( SELECT MAX(o2.order_date)
        FROM order o2
        WHERE o2.userid = o.userid
          AND o2.orderType = '0'
      )

or

SELECT o.* 
FROM order o
  JOIN
    ( SELECT userid
           , MAX(order_date) AS lastPurchaseDate
      FROM order 
      WHERE o.orderType ='0'
      GROUP BY userid
    ) AS grp
    ON grp.userid = o.userid
    AND grp.lastPurchaseDate = o.order_date