问题
I need to do something really weird, which is to create fake records in a view to fill the gap between posted dates of product prices.
Actually, my scenario is a little bit more complicated than that, but I've simplified to products/dates/prices.
Let's say we have this table:
create table PRICES_TEST
(
PRICE_DATE date not null,
PRODUCT varchar2(13) not null,
PRICE number
);
alter table PRICES_TEST
add constraint PRICES_TEST_PK
primary key (PRICE_DATE, PRODUCT);
With these records:
insert into PRICES_TEST values (date'2012-04-15', 'Screw Driver', 13);
insert into PRICES_TEST values (date'2012-04-18', 'Screw Driver', 15);
insert into PRICES_TEST values (date'2012-04-13', 'Hammer', 10);
insert into PRICES_TEST values (date'2012-04-16', 'Hammer', 15);
insert into PRICES_TEST values (date'2012-04-19', 'Hammer', 17);
selecting records will return me this:
PRICE_DATE PRODUCT PRICE
------------------------- ------------- ----------------------
13-Apr-2012 00:00:00 Hammer 10
16-Apr-2012 00:00:00 Hammer 15
19-Apr-2012 00:00:00 Hammer 17
15-Apr-2012 00:00:00 Screw Driver 13
18-Apr-2012 00:00:00 Screw Driver 15
Assuming today is Apr 21 2012, I need a view that shall repeat each price every day until a new price is posted. Like this:
PRICE_DATE PRODUCT PRICE
------------------------- ------------- ----------------------
13-Apr-2012 00:00:00 Hammer 10
14-Apr-2012 00:00:00 Hammer 10
15-Apr-2012 00:00:00 Hammer 10
16-Apr-2012 00:00:00 Hammer 15
17-Apr-2012 00:00:00 Hammer 15
18-Apr-2012 00:00:00 Hammer 15
19-Apr-2012 00:00:00 Hammer 17
20-Apr-2012 00:00:00 Hammer 17
21-Apr-2012 00:00:00 Hammer 17
15-Apr-2012 00:00:00 Screw Driver 13
16-Apr-2012 00:00:00 Screw Driver 13
17-Apr-2012 00:00:00 Screw Driver 13
18-Apr-2012 00:00:00 Screw Driver 15
19-Apr-2012 00:00:00 Screw Driver 15
20-Apr-2012 00:00:00 Screw Driver 15
21-Apr-2012 00:00:00 Screw Driver 15
Any ideas how to do that? I cannot really use other auxiliary tables, triggers nor PL/SQL programming, I really need to do this using a view.
I think this can be done using oracle analytics, but I'm not familiar with that. I tried to read this http://www.club-oracle.com/articles/analytic-functions-i-introduction-164/ but I didn't get it at all.
回答1:
I think I have a solution using an incremental approach toward the final result with CTE's:
with mindate as
(
select min(price_date) as mindate from PRICES_TEST
)
,dates as
(
select mindate.mindate + row_number() over (order by 1) - 1 as thedate from mindate,
dual d connect by level <= floor(SYSDATE - mindate.mindate) + 1
)
,productdates as
(
select p.product, d.thedate
from (select distinct product from PRICES_TEST) p, dates d
)
,ranges as
(
select
pd.product,
pd.thedate,
(select max(PRICE_DATE) from PRICES_TEST p2
where p2.product = pd.product and p2.PRICE_DATE <= pd.thedate) as mindate
from productdates pd
)
select
r.thedate,
r.product,
p.price
from ranges r
inner join PRICES_TEST p on r.mindate = p.price_date and r.product = p.product
order by r.product, r.thedate
mindateretrieves the earliest possible date in the data setdatesgenerates a calendar of dates from earliest possible date to today.productdatescross joins all possible products with all possible datesrangesdetermines which price date applied at each date- the final query links which price date applied to the actual price and filters out dates for which there are no relevant price dates via the
inner joincondition
Demo: http://www.sqlfiddle.com/#!4/e528f/126
回答2:
You can create a row generator statement using the CONNECT BY LEVEL syntax, cross joined with the distinct products in your table, and then outer join that to your prices table. The final touch is to use the LAST_VALUE function and IGNORE NULLS to repeat the price until a new value is encountered, and since you wanted a view, with a CREATE VIEW statement:
create view dense_prices_test as
select
dp.price_date
, dp.product
, last_value(pt.price ignore nulls) over (order by dp.product, dp.price_date) price
from (
-- Cross join with the distinct product set in prices_test
select d.price_date, p.product
from (
-- Row generator to list all dates from first date in prices_test to today
with dates as (select min(price_date) beg_date, sysdate end_date from prices_test)
select dates.beg_date + level - 1 price_date
from dual
cross join dates
connect by level <= dates.end_date - dates.beg_date + 1
) d
cross join (select distinct product from prices_test) p
) dp
left outer join prices_test pt on pt.price_date = dp.price_date and pt.product = dp.product;
回答3:
I made a few changes to Wolf's excellent answer.
I replaced the subquery factoring (WITH) with a regular subquery in the connect by. This makes the code a little simpler. (Although this type of code looks weird at first either way, so there may not be a huge gain here.)
Most significantly, I used a partition outer join instead of a cross join and outer join. Partition outer joins are also kind of strange, but they are meant for exactly this type of situation. This makes the code simpler, and should improve performance.
select
price_dates.price_date
,product
,last_value(price ignore nulls) over (order by product, price_dates.price_date) price
from
(
select trunc(sysdate) - level + 1 price_date
from dual
connect by level <= trunc(sysdate) -
(select min(trunc(price_date)) from prices_test) + 1
) price_dates
left outer join prices_test
partition by (prices_test.product)
on price_dates.price_date = prices_test.price_date;
回答4:
I just realized that @Wolf and @jonearles improvements do not return the exact results I needed because the row generator to list all dates won't generate the ranges by product. If the first price of product A is later than any price of product B the first listed date of product A still must be the same. But they really helped me to work further and get the expected results:
I started with changing @wolf's date range selector from this:
select min(price_date) beg_date, sysdate end_date from prices_test
to this:
select min(PRICE_DATE) START_DATE, sysdate as END_DATE, PRODUCT
from PRICES_TEST group by sysdate, PRODUCT
But, somehow, the number of rows per product is exponentially growing repeatedly for each level. I just added a distinct in the outter query. The finally select was this:
select
DP.PRICE_DATE,
DP.PRODUCT,
LAST_VALUE(PT.PRICE ignore nulls) over (order by DP.PRODUCT, DP.PRICE_DATE) PRICE
from (
select distinct START_DATE + DAYS as PRICE_DATE, PRODUCT
from
(
-- Row generator to list all dates from first date of each product to today
with DATES as (select min(PRICE_DATE) START_DATE, sysdate as END_DATE, PRODUCT from PRICES_TEST group by sysdate, PRODUCT)
select START_DATE, level - 1 as DAYS, PRODUCT
from DATES
connect by level < END_DATE - START_DATE + 1
order by 3, 2
) d order by 2, 1
) DP
left outer join prices_test pt on pt.price_date = dp.price_date and pt.product = dp.product;
@Mellamokb solution is actually what I really need and is certainly better than my noobie solution.
Thank's everyone not only for helping me with this but also for presenting me features such as "with" and "connect by".
来源：https://stackoverflow.com/questions/10254769/duplicating-records-to-fill-gap-between-dates