Best way to flatten out this table?

Question

Lets say you're dealing with these two tables:
CREATE TABLE VEHICLES
VEHICLE_ID NUMBER,
VEHICLE_NAME VARCHAR2(100 BYTE),
MILES NUMBER
CREATE TABLE VEHICLE_PARTS
PART_ID NUMBER,
VEHICLE_ID NUMBER NOT NULL,
PART_TYPE NUMBER NOT NULL,
PART_DESCRIPTION VARCHAR2(1000 BYTE) NOT NULL,
START_SERVICE_DATE DATE NOT NULL,
END_SERVICE_DATE DATE,
PART_TYPE_NAME VARCHAR2(100 BYTE)
And some example data as follows:
Insert into VEHICLES (VEHICLE_ID, VEHICLE_NAME, MILES) Values (1, 'Honda Civic', 75500);
Insert into VEHICLES (VEHICLE_ID, VEHICLE_NAME, MILES) Values (2, 'Ford Taurus', 156000);
Insert into VEHICLE_PARTS
(PART_ID, VEHICLE_ID, PART_TYPE, PART_DESCRIPTION, START_SERVICE_DATE, END_SERVICE_DATE, PART_TYPE_NAME)
Values
(1, 1, 1, '1.4 VTEC',
TO_DATE('07/07/2009 00:00:00', 'MM/DD/YYYY HH24:MI:SS'), TO_DATE('05/03/2010 00:00:00', 'MM/DD/YYYY HH24:MI:SS'), 'ENGINE');
Insert into VEHICLE_PARTS
(PART_ID, VEHICLE_ID, PART_TYPE, PART_DESCRIPTION, START_SERVICE_DATE, PART_TYPE_NAME)
Values
(2, 1, 1, '1.6 VTEC',
TO_DATE('05/03/2010 00:00:00', 'MM/DD/YYYY HH24:MI:SS'), 'ENGINE');
Insert into VEHICLE_PARTS
(PART_ID, VEHICLE_ID, PART_TYPE, PART_DESCRIPTION, START_SERVICE_DATE, END_SERVICE_DATE, PART_TYPE_NAME)
Values
(3, 1, 2, 'Good Year All-Season',
TO_DATE('07/07/2009 00:00:00', 'MM/DD/YYYY HH24:MI:SS'), TO_DATE('08/10/2010 00:00:00', 'MM/DD/YYYY HH24:MI:SS'), 'TIRES');
Insert into VEHICLE_PARTS
(PART_ID, VEHICLE_ID, PART_TYPE, PART_DESCRIPTION, START_SERVICE_DATE, PART_TYPE_NAME)
Values
(4, 1, 2, 'Bridgestone Blizzaks',
TO_DATE('08/10/2010 00:00:00', 'MM/DD/YYYY HH24:MI:SS'), 'TIRES');
Insert into VEHICLE_PARTS
(PART_ID, VEHICLE_ID, PART_TYPE, PART_DESCRIPTION, START_SERVICE_DATE, PART_TYPE_NAME)
Values
(5, 2, 1, '3.5 L Duratec',
TO_DATE('06/01/2008 00:00:00', 'MM/DD/YYYY HH24:MI:SS'), 'ENGINE');
Insert into VEHICLE_PARTS
(PART_ID, VEHICLE_ID, PART_TYPE, PART_DESCRIPTION, START_SERVICE_DATE, END_SERVICE_DATE, PART_TYPE_NAME)
Values
(6, 2, 2, 'Good Year All-Season',
TO_DATE('06/01/2008 00:00:00', 'MM/DD/YYYY HH24:MI:SS'), TO_DATE('03/15/2009 00:00:00', 'MM/DD/YYYY HH24:MI:SS'), 'TIRES');
Insert into VEHICLE_PARTS
(PART_ID, VEHICLE_ID, PART_TYPE, PART_DESCRIPTION, START_SERVICE_DATE, END_SERVICE_DATE, PART_TYPE_NAME)
Values
(7, 2, 2, 'Michelin All-Seaon',
TO_DATE('03/15/2009 00:00:00', 'MM/DD/YYYY HH24:MI:SS'), TO_DATE('01/12/2011 00:00:00', 'MM/DD/YYYY HH24:MI:SS'), 'TIRES');
Insert into VEHICLE_PARTS
(PART_ID, VEHICLE_ID, PART_TYPE, PART_DESCRIPTION, START_SERVICE_DATE, PART_TYPE_NAME)
Values
(8, 2, 2, 'Nokian',
TO_DATE('01/12/2011 00:00:00', 'MM/DD/YYYY HH24:MI:SS'), 'TIRES');
And you need to produce a view which displays the joined data flattened out where each vehicle has one row with columns representing their most current part (by what has a service start date with null end date).
Like this:
Vehicle: Engine: Tires:
Honda Civic 1.6 VTEC Bridgestone Blizzaks
Ford Taurus 3.5 L Duratec Nokian
Is there a fast/efficient way to do this?
My current approach which is the brute force method is to have a separate outer join for each column I need to pull with condition of max(START_SERVICE_DATE) to get the current part for each type (Engine, Tires, etc...).
but its so slow and painful code.
i thought about Pivot but I dont think Pivot would help here since there is no aggregation going on, right?
Could anything with partition over help? Im not familiar with that syntax

Answer 1

Hi,
trant wrote:
Your query does work great I just ran it - but by your last note about wanting to use SELECT...PIVOT - would you please elaborate on that?If you're used to doing pivots with CASE (or DECODE) and GROUP BY, then you may require some practice before the new way seems better. I beliieve it is, and I think you'll find whatever effort you have to spend in learning to use the new PIVOT feature is time well invested. I find this code:
WITH     got_r_num     AS
     SELECT     v.vehicle_name
     ,     vp.part_description
     ,     vp.part_type_name
     ,     ROW_NUMBER () OVER ( PARTITION BY  vp.vehicle_id
                         ,             vp.part_type_name
                         ORDER BY        start_service_date
                       )     AS r_num
     FROM     vehicle_parts     vp
     JOIN     vehicles     v     ON     v.vehicle_id     = vp.vehicle_id
     WHERE     vp.end_service_date     IS NULL
SELECT       vehicle_name, engine, tires
FROM       got_r_num
PIVOT       (     MIN (part_description)
       FOR     part_type_name  IN ( 'ENGINE'     AS engine
                         , 'TIRES'     AS tires
WHERE       r_num     = 1
ORDER BY  vehicle_name
;easier to understand and maintain, and this is a more complicated than average example. Often, when using SELECT ... PIVOT, the main SELECT clause is juSt "SELECT *", and adding more columns is even easier. For eaxample:
WITH     got_r_num     AS
     SELECT     v.vehicle_name
     ,     vp.part_description
     ,     vp.part_type_name
     ,     ROW_NUMBER () OVER ( PARTITION BY  vp.vehicle_id
                         ,             vp.part_type_name
                         ORDER BY        start_service_date
                       )     AS r_num
     FROM     vehicle_parts     vp
     JOIN     vehicles     v     ON     v.vehicle_id     = vp.vehicle_id
     WHERE     vp.end_service_date     IS NULL
,     top_1_only     AS
     SELECT     vehicle_name
     ,     part_description
     ,     part_type_name
     FROM     got_r_num
     WHERE     r_num     = 1
SELECT       *
FROM       top_1_only
PIVOT       (     MIN (part_description)
       FOR     part_type_name  IN ( 'ENGINE'
                         , 'TIRES'
ORDER BY  vehicle_name
;If you want to include BRAKES and STEERING columns, all you have to do is change
FOR     part_type_name  IN ( 'ENGINE', 'TIRES')to
FOR     part_type_name  IN ( 'ENGINE', 'TIRES', 'BRAKES', 'STEERING')The only way it could be any easier is if it were automatic! (That's another subject entirely.)