sql - 使用计算值枚举两个日期之间的年份

Question

我有一个看起来像这样的 postgres 表:

proposal_id | nih_budget_start | nih_budget_end  | nsf_start_date | nsf_end_date   | award_amount
proposal_A  | 03/01/2000       | 12/31/2000      |                |                | 10,000
proposal_B  |                  |                 | 08/01/2005     | 07/31/2009     | 5,000,000
proposal_C  | 06/27/2012       | 11/17/2013      |                |                | 420,000

日期具有 date 数据类型。

我想创建一个 View ，告诉我该提案每年获得资助，以及平均奖励金额是多少。因此， View 可能看起来像这样(选项 1):

proposal_id | start_year | end_year | average_award
proposal_A  | 2000       | 2000     | 10,000
proposal_B  | 2005       | 2009     | 1,000,000 
proposal_C  | 2012       | 2013     | 210,000

或者——甚至更好——这个(选项 2):

proposal_id | year | award
proposal_A  | 2000 | 10,000
proposal_B  | 2005 | 1,000,000
proposal_B  | 2006 | 1,000,000
proposal_B  | 2007 | 1,000,000
proposal_B  | 2008 | 1,000,000
proposal_B  | 2009 | 1,000,000
proposal_C  | 2012 | 210,000
proposal_C  | 2023 | 210,000

此外，为部分年度资助按比例分配奖励金额可能会很好，但这并非完全必要。

根据下面建议的答案，我目前正在这样做，它似乎按预期工作以获得上面的选项 1:

CREATE VIEW award_per_year AS
select t1.proposal_id,t1.START_DATE,t1.END_DATE,
(t1.adjusted_award_amount/((t1.END_DATE - t1.START_DATE) + 1.)) avg_award
from
(select t2.proposal_id,
(extract(year from START_DATE)) START_DATE,
(extract(year from END_DATE)) END_DATE,
t2.adjusted_award_amount from
(select proposal_id,
case when nih_budget_start is not NULL then nih_budget_start else nsf_start_date end start_date,
case when nih_budget_end is not NULL then nih_budget_end else nsf_end_date end end_date,
adjusted_award_amount from proposal)t2)t1

Answer 1

选项 1:使用 COALESCE

SELECT proposal_id, start_year, end_year
     , award_amount/((end_year - start_year) + 1.0) AS avg_award
FROM  (
   SELECT proposal_id
        , extract(year FROM COALESCE(nih_budget_start, nsf_start_date))::int AS start_year
        , extract(year FROM COALESCE(nih_budget_end, nsf_end_date))::int AS end_year
        , award_amount
   FROM   proposal
   ) sub;

选项 2:使用 generate_series()

SELECT proposal_id
     , generate_series(start_year, end_year) AS year
     , award_amount/((end_year - start_year) + 1.0) AS avg_award
FROM  (
   SELECT proposal_id
        , extract(year FROM COALESCE(nih_budget_start, nsf_start_date))::int AS start_year
        , extract(year FROM COALESCE(nih_budget_end, nsf_end_date))::int AS end_year
        , award_amount
   FROM   proposal
   ) sub;

-> SQLfiddle