计算具有上一日期期初余额的值的总和

Question

I have the following table which you can also find in the SQL fiddle here :

CREATE TABLE Flows (
    Flow_Date DATE,
    Product TEXT,
    FlowType TEXT,
    Quantity VARCHAR(255)
);

INSERT INTO Flows
(Flow_Date, Product, FlowType, Quantity)
VALUES 
("2019-05-23", "Product A", "Inbound", "400"),
("2019-05-23", "Product B", "Inbound", "500"),
("2019-05-23", "Product A", "Outbound", "300"),
("2019-05-23", "Product B", "Outbound", "200"),
("2019-05-23", "Product A", "Stock", "100"),
("2019-05-23", "Product B", "Stock", "300"),
("2019-06-19", "Product A", "Inbound", "900"),
("2019-06-19", "Product B", "Inbound", "800"),
("2019-06-19", "Product A", "Outbound", "650"),
("2019-06-19", "Product B", "Outbound", "400"),
("2019-06-19", "Product A", "Stock", "350"),
("2019-06-19", "Product B", "Stock", "700");

I use the following query to get information data from the table:

SELECT
 Flow_Date,
 SUM(Stock) AS Stock,
 SUM(Inbound + Outbound*-1) AS Stock_Calculated,
 SUM(Inbound) AS Inbound,
 SUM(Outbound) AS Outbound
 FROM

  (SELECT 
    Flow_Date, 
    sum(case when FlowType = 'Stock' then Quantity else 0 end) Stock,
    sum(case when FlowType = 'Inbound' then Quantity else 0 end) Inbound,
    sum(case when FlowType = 'Outbound' then Quantity else 0 end) Outbound
   FROM Flows
   GROUP BY 1) Flows

 GROUP BY 1

+------------+-------+------------------+---------+----------+
| Flow_Date  | Stock | Stock_Calculated | Inbound | Outbound |
+------------+-------+------------------+---------+----------+
| 2019-05-23 |   400 |              400 |     900 |      500 |
| 2019-06-19 |  1050 |              650 |    1700 |     1050 |
+------------+-------+------------------+---------+----------+

All this works exactly how I need it.

---

However, now my issue is the line SUM(Inbound + Outbound*-1) AS Stock_Calculated .
Basically, I want to achive that the Stock is calculated by the Inbounds and Outbounds .
For this I also have to include an Opening Balance for the stock.

Opening Balance + Inbounds - Outbounds = Closing Balance (--> Opening Balance for next date)

The result should look like this:

Flow_Date       Stock     Stock_Calculated      Inbound      Outbound
2019-05-23        400          400*               900           500
2019-06-19      1.000        1.000**            1.700         1.100

* 0 + 900 - 500 = 400
** 400 + 1.700 - 1.100 = 1.000

What do I have to change in my code to make it work?

Answer 1

MySQL 5+

SELECT Flow_Date, 
       Stock,
       @Stock := @Stock + Inbound - Outbound Stock_Calculated,
       Inbound,
       Outbound
FROM ( SELECT Flow_Date,
              SUM(case when FlowType = 'Stock' 
                       then Quantity 
                       else 0 end) AS Stock,
              SUM(case when FlowType = 'Inbound' 
                       then Quantity 
                       else 0 end) AS Inbound,
              SUM(case when FlowType = 'Outbound'       
                       then Quantity 
                       else 0 end) AS Outbound
        FROM Flows
        GROUP BY Flow_Date ) Flows, 
      ( SELECT @Stock := 0 ) init_variable
ORDER BY Flow_Date;

MySQL 8+:

SELECT Flow_Date, 
       Stock,
       SUM(Inbound) OVER (ORDER BY Flow_Date) - SUM(Outbound) OVER (ORDER BY Flow_Date) Stock_Calculated,
       Inbound,
       Outbound
FROM ( SELECT Flow_Date,
              SUM(case when FlowType = 'Stock' 
                       then Quantity 
                       else 0 end) AS Stock,
              SUM(case when FlowType = 'Inbound' 
                       then Quantity 
                       else 0 end) AS Inbound,
              SUM(case when FlowType = 'Outbound'       
                       then Quantity 
                       else 0 end) AS Outbound
        FROM Flows
        GROUP BY Flow_Date ) Flows;

fiddle

Answer 2

You can mix window functions and aggregations, so:

select Flow_Date, 
    sum(case when FlowType = 'Stock' then Quantity else 0 end) as Stock,
    sum(case when FlowType = 'Inbound' then Quantity else 0 end) as Inbound,
    sum(case when FlowType = 'Outbound' then Quantity else 0 end) as Outbound,
    sum(case when FlowType = 'Inbound' then Quantity
             when FlowType = 'Outbound' then -Quantity
             else 0
        end) over (order by date) as calculated_stock
from Flows
group by 1;