上一行結束日期作為 SQL 中的下一行開始日期

Question

需要一些幫助請，

我有一個名為“hist_lastupdated”的字段，其中包含產品價格修改的最后更新日期。

基於此字段，我想提取修改的開始日期和結束日期。

事實上我有這個：

**Product_id , Price ,        hist_lastupdated**
284849       18.95          2015-05-29 00:53:55
284849       15.95          2015-08-14 01:04:46
284849       18.95          2016-06-11 00:50:31
284849       15.95          2016-08-24 00:45:11

我想得到這樣的結果：

**Product_id , Price ,   hist_lastupdated    ,start_date  ,           End_date**
284849  18.95  2015-05-29 00:53:55  2014-05-01 00:00:00   2015-05-29 00:53:55  
284849  15.95  2015-08-14 01:04:46  2015-05-29 00:53:55   2015-08-14 01:04:46
284849  18.95  2016-06-11 00:50:31  2015-08-14 01:04:46   2016-06-11 00:50:31
284849  15.95  2016-08-24 00:45:11  2016-06-11 00:50:31   2016-08-24 00:45:11

兩個字，開始日期是上一行的結束日期我有很多產品id

Answer 1

像這樣的東西：

select Product_id, 
       Price,        
       hist_lastupdated, 
       lag(hist_lastupdated) over (partition by product_id order by hist_lastupdated) as start_date, 
       hist_lastupdated as end_date
from the_table

您沒有解釋第一列的 start_date 是在哪里計算的。 如果那是從hist_lastupdated開始的月初，您可以執行以下操作：

lag(hist_lastupdated, 1, date_trunc('month', hist_lastupdated)) over (...)

Answer 2

我不確定您將如何僅使用 SQL 來執行此操作，但是如果您能夠編寫一些腳本，則可以編寫一個類似於以下內容的快速程序（偽代碼）：

lines = execute(SELECT product_id, price, hist_lastupdated FROM ProductTable)

startDate = 00:00:00 2014-05-01

outputLines = []

for row in lines:

    outLine = []
    outline.append(row[0])
    outline.append(row[1])
    outline.append(row[2])
    outline.append(startDate)
    outline.append(row[2])

    startDate = row[2]

#Now do what you want with the output you have in a nice list of lists in the format you need, insert into a different table, write to a file, whatever you want.

Answer 3

我會在 MS SQL Server 中使用這些解決方案之一。 希望其中之一適用於您的問題。

純 SQL 語句如下所示：

select
    t.product_id, t.price, s.start_date, t.end_date
from 
    product t
    outer apply
    (
        select top 1 
            end_date start_date
        from
            product o
        where
            o.end_date < t.end_date
        order by
            o.end_date desc
    ) s

即使具有良好的索引，對返回的每條記錄的交叉應用也可能是一個性能問題。

如果您的 SQL 服務器支持 LAG 功能：

select
    t.product_id, t.price, 
    LAG(T.end_date) over (order by t.end_date),
    t.end_date
from 
    product t

或者您可能會找到一種方法對更新語句中的變量執行相同的操作，以“記住”先前更新記錄中的值，如 T-SQL：

-- Insert the desired output into a table variable that also has a start_date field.
-- Be sure to insert the records ordered by the date value.

declare @output table (product_id int, price numeric(10,2), [start_date] datetime, [end_date] datetime)

insert @output (product_id, price, end_date)
select 1, 10, '1/1/2015'
union all select  2, 11, '2/1/2015'
union all select 3, 15, '3/1/2015'
union all select 4, 20, '4/1/2015'
order by 3

-- Update the start date using the end date from the previous record
declare @start_date datetime, @end_date datetime

update 
    @output
set
    @start_date = @end_date,
    @end_date = end_date,
    start_date = @start_date

select * from @output

我認為 Microsoft 不推薦這種技術，但它對我很有用並且一直有效。 我只對表變量使用了這種技術。 我不太願意相信實際表中記錄的更新順序。 現在我會改用 LAG() 。

Answer 4

這是我找到的解決方案，我想使用滯后功能，但結果不是我想要的。

解決方案 ：

WITH 
price_table_1 as (
   select
   -1 + ROW_NUMBER() over (partition by t1.product_id,t1.id ,t1.channel_id)  as rownum_w1,
   t1.id,
   t1.product_id,
   t1.channel_id,
   t1.member_id,
   t1.quantity,
   t1.price,
   t1.promo_dt_start,
   t1.promo_dt_end,
   t1.hist_lastupdated
FROM dwh_prod.hist_prices t1
where   t1.channel_id='1004' and t1.product_id = '5896'  and t1.quantity = '1' and t1.promo_dt_start is null
order by t1.product_id,t1.channel_id,t1.hist_lastupdated
),price_table_2 as (
   select
   ROW_NUMBER() over (partition by t2.product_id,t2.id ,t2.channel_id) as     rownum_w2,
   t2.id,
   t2.product_id,
   t2.channel_id,
   t2.member_id,
   t2.quantity,
   t2.price,
   t2.promo_dt_start,
   t2.promo_dt_end,
   t2.hist_lastupdated
FROM dwh_prod.hist_prices t2
where    t2.channel_id='1004' and t2.product_id = '5896'  and t2.quantity = '1' and t2.promo_dt_start is null
order by t2.product_id,t2.channel_id,t2.hist_lastupdated
)

   select
   t1.id,
   t1.product_id,
   t1.channel_id,
   t1.member_id,
   t1.quantity,
   t1.price,
   t1.promo_dt_start,
   t1.promo_dt_end,
   t2.hist_lastupdated as start_date,
   t1.hist_lastupdated as end_date

FROM price_table_1 t1
inner join price_table_2 t2
on t2.product_id = t1.product_id and t2.id = t1.id and t2.channel_id =        t1.channel_id
and rownum_w1 = (rownum_w2)
UNION ALL
select
   t1.id,
   t1.product_id,
   t1.channel_id,
   t1.member_id,
   t1.quantity,
   t1.price,
   t1.promo_dt_start,
   t1.promo_dt_end,
   CONVERT(TIMESTAMP,'2014-01-01') as start_date,
   t1.hist_lastupdated as end_date

FROM price_table_1 t1 
where rownum_w1 = '0';