复制记录以填补日期之间的差距

Question

我需要做一些非常奇怪的事情,即在视图中创建虚假记录以填补产品价格的发布日期之间的差距.

实际上,我的情况比这复杂一点,但我已经简化为产品/日期/价格.

假设我们有这张表:

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);

有了这些记录:

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);

选择记录将返回给我:

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                     

假设今天是2012年4月21日,我需要一个视图,每天重复每个价格,直到新价格发布.像这样:

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                     

任何想法如何做到这一点？我不能真正使用其他辅助表,触发器或PL/SQL编程,我真的需要使用视图来做到这一点.

我认为这可以使用oracle分析完成,但我不熟悉.我试着读这个http://www.club-oracle.com/articles/analytic-functions-i-introduction-164/,但我根本没有得到它.

Answer 1

您可以使用CONNECT BY LEVEL语法创建行生成器语句,与表中的不同产品交叉连接,然后将外部连接到您的价格表.最后一步是使用该LAST_VALUE函数并IGNORE NULLS重复价格直到遇到新值,并且因为您想要一个视图,并带有一个CREATE VIEW语句:

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;

Answer 2

我想我有一个解决方案，使用增量方法来获得 CTE 的最终结果：

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

• mindate 检索数据集中可能的最早日期
• dates 生成从最早日期到今天的日期日历。
• productdates 交叉连接所有可能的产品和所有可能的日期
• ranges 确定在每个日期应用的价格日期
• 最终查询链接哪个价格日期适用于实际价格，并通过inner join条件过滤掉没有相关价格日期的日期

演示：http : //www.sqlfiddle.com/#!4/ e528f/ 126