比较日期范围的最新值？ (SQL/Snowflake)

Question

我有值 Table-A 喜欢：

Patient|Invoice|Date
A,111,2021-02-01
A,222,2021-01-01
B,333,2021-03-01
B,444,2021-02-01
C,555,2021-04-01
C,666,2021-03-01

Table-B 中的值如：

Patient|Value|Date
A,2,2021-01-05
A,3,2021-01-05
A,3,2021-02-05
B,1,2021-02-05
B,1,2021-03-05
C,6,2021-01-01

我想加入这两个表，以便我可以看到 Table-B 中截至日期 Table-A 中给定患者的最新累积值总和。

Patient|Invoice|Latest Value|Date
A,111,5,2021-02-01
A,222,0,2021-01-01
B,333,1,2021-03-01
B,444,0,2021-02-01
C,555,6,2021-04-01
C,666,6,2021-03-01

我如何按日期连接这两个表才能完成此操作？

Answer 1

第一步似乎是基本的 SQL 加入：

select patient, invoice, sum(value), date
from table1 a
join table2 b
on a.patient=b.patient
and a.date=b.date
group by patient, invoice, date

但是您可以应用 sum() over():

而不是普通的 sum()

select patient, invoice
  , sum(value) over(partition by patient order by date)
  , date
from table1 a
join table2 b
on a.patient=b.patient
and a.date=b.date
group by patient, invoice, date

Answer 2

我认为首先我们需要计算发票有效的时间间隔（使用LAG function), then calculate the cumulative SUM。

WITH A AS (
  SELECT Patient, Invoice, Date, IFNULL(LAG(Date) OVER(PARTITION BY Patient ORDER BY Date), '1900-01-01') AS LG
    FROM Table_A
)
SELECT DISTINCT A.Patient, A.Invoice, IFNULL(SUM(B.Value) OVER(PARTITION BY A.Patient ORDER BY A.Date), 0) AS Latest_Value, A.Date
  FROM A
  LEFT JOIN Table_B AS B 
    ON A.Patient = B.Patient
   AND B.Date >= A.LG AND B.Date < A.Date
GROUP BY A.Patient, A.Invoice, A.Date, B.Value
ORDER BY A.Patient, A.Invoice, A.Date;

比较日期范围的最新值？ (SQL/Snowflake)

Latest value of compared date range? (SQL/Snowflake)

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