在查询结果中将先前日期的值添加到实际日期

Posted 2023-02-16

【中文标题】在查询结果中将先前日期的值添加到实际日期

【英文标题】：Add value with previous date to actual date in query result

【发布时间】：2020-08-10 20:31:17

【问题描述】：

DB-Fiddle:

CREATE TABLE logistics (
    id int auto_increment primary key,
    flow_date DATE,
    flow_type VARCHAR(255),
    flow_quantity INT
);

INSERT INTO logistics
(flow_date, flow_type, flow_quantity
)
VALUES 
("2020-04-18", "inbound", "500"),
("2020-04-18", "outbound", "400"),
("2020-04-18", "stock", "100"),
("2020-04-19", "inbound", "800"),
("2020-04-19", "outbound", "650"),
("2020-04-19", "stock", "250"),
("2020-04-20", "inbound", "730"),
("2020-04-20", "outbound", "600"),
("2020-04-20", "stock", "380"),
("2020-04-21", "inbound", "420"),
("2020-04-21", "outbound","370"),
("2020-04-21", "stock", "430");

预期结果：

flow_date     stock_yesterday   inbound    outbound    stock_today
2020-04-18         0              500        -400         100        
2020-04-19        100             800        -650         250
2020-04-20        250             730        -600         380
2020-04-21        380             420        -370         430

---

基本上，在我的结果中，我想展示这个时间线：stock_yesterday + inbound - outbound = stock_today。 因此，我需要将原始表格更改如下：

a) flow_types 在结果中用作columns。 a) stock_yesterday 是前一天的 flow_type stock 的 flow_quantity。 b) 所有其他flow_types 引用相同的flow_date。

---

到目前为止，我想出了这个查询，但无法使它工作：

SELECT
flow_date,
(CASE WHEN flow_type = "inbound" THEN flow_quantity END) AS inbound,
(CASE WHEN flow_type = "outbound" THEN flow_quantity END) AS outbound,
(CASE WHEN flow_type = "stock" THEN flow_quantity END) AS stock_today
FROM logistics
GROUP BY 1;

它只显示inbound。 我也不知道如何将stock_yesterday 添加到查询中。

我需要对查询进行哪些更改才能获得预期结果？

【问题讨论】：

如果你已经有了stock，为什么还要计算它？

【参考方案1】：

您可以使用窗口函数和聚合：

select
    flow_date,
    sum(inbound + outbound) 
        over(order by flow_date rows between unbounded preceding and 1 preceding) stock_yesterday,
    inbound,
    outbound,
    sum(inbound + outbound) over(order by flow_date) stock_today
from (
    select 
        flow_date,
        sum(case when flow_type = 'inbound' then flow_quantity else 0 end) inbound,
        sum(case when flow_type = 'outbound' then -flow_quantity else 0 end) outbound
    from logistics
    group by flow_date
) t
order by flow_date

子查询不是绝对必要的，但它有助于缩短语法。

Demo on DB Fiddle：

flow_date |股票_昨天 |入境 |出境 |今日股票 :--------- | --------------: | ------: | --------: | ----------: 2020-04-18 | 空 | 500 | -400 | 100 2020-04-19 | 100 | 800 | -650 | 250 2020-04-20 | 250 | 730 | -600 | 380 2020-04-21 | 380 | 420 | -370 | 430