仅数据库 使用条件运行总计

Question

有很多关于使用 Postgres 计算运行总数的问题，但我正在努力做一些稍微不同的事情。

我有一张像这样的表

txn_id	amount
String	Integer

amounts 可以是正数也可以是负数。

我正在尝试返回一个看起来像这样的表

txn_id	amount	running_total	overage_total
String	Integer	Integer	Integer

其中运行总计是 amount 列的运行总和，只要金额大于零，overage_total 是低于零的金额的运行总和。

一个例子是

txn_id	amount
a	1
b	2
c	-4
d	2
e	-1

我一直在使用窗口函数来计算运行总和，但这并不是我们所需要的。

正确的表格会返回

txn_id	amount	running_total	overage_total
a	1	1	0
b	2	3	0
c	-4	0	1
d	2	2	1
e	-1	1	1

目前我正在代码中执行此操作，但如果可能的话，在数据库中执行此操作真的很不可思议。

Answer 1

这里的模式是总有一个上限。可以通过递归 cte 来实现：

WITH RECURSIVE cte_r AS (
  SELECT t.*, ROW_NUMBER() OVER(ORDER BY t.txn_id) AS rn FROM tab t
), cte AS (
  SELECT rn,
         txn_id,
         amount, 
         CASE WHEN amount <= 0 THEN 0 ELSE amount END AS total,
         CASE WHEN amount <= 0 THEN 1 ELSE 0 END AS overage_total
  FROM cte_r
  WHERE rn = 1
  UNION ALL
  SELECT cte_r.rn,
         cte_r.txn_id,
         cte_r.amount,
         CASE WHEN cte.total + cte_r.amount <= 0 THEN 0 
                        ELSE cte.total + cte_r.amount 
                   END AS total,
         cte.overage_total + CASE WHEN cte.total + cte_r.amount <= 0 
                                  THEN 1 ELSE 0 END AS overage_total
  FROM cte
  JOIN cte_r
    ON cte.rn = cte_r.rn-1
)
SELECT txn_id, amount, total,overage_total
FROM cte
ORDER BY rn;

输出：

+---------+---------+--------+---------------+
| txn_id  | amount  | total  | overage_total |
+---------+---------+--------+---------------+
| a       |      1  |     1  |             0 |
| b       |      2  |     3  |             0 |
| c       |     -4  |     0  |             1 |
| d       |      2  |     2  |             1 |
| e       |     -1  |     1  |             1 |
| f       |      2  |     3  |             1 |
| h       |     -4  |     0  |             2 |
+---------+---------+--------+---------------+

db<>fiddle demo

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相关：Conditional SUM on Oracle 和 7. Capping a running total

Answer 2

一种选择是使用函数来逐行遍历并进行计算：

CREATE FUNCTION runningTotalWithCondition() RETURNS TABLE(txn_id char(1), amount int, running_total integer, overage_total integer) AS
$$

DECLARE 

running_total integer := 0;
overage_total integer := 0;
c CURSOR FOR SELECT * FROM t ORDER BY txn_id ASC;

BEGIN
    
    FOR recordvar IN c LOOP
      IF (running_total + recordvar.amount) > 0 THEN
        running_total = running_total + recordvar.amount;
        overage_total = overage_total;
      ELSE 
        overage_total = overage_total + abs(running_total + recordvar.amount);
        running_total = 0;
      END IF;
    
      RETURN QUERY SELECT recordvar.txn_id, recordvar.amount, running_total, overage_total;
    END LOOP;

END;

$$ LANGUAGE plpgsql;

调用函数：

SELECT * FROM runningTotalWithCondition();