sql - 如何对具有重置条件的列进行 SUM()？

Question

我使用的是 Postgresql 9.2，我需要从 buttom 向上求和初始值为 100 的数量，但是如果我遇到名称为 X 的行，我需要从该行中的 qty 值重新开始求和。

例如:

itemorder   name    qty
  1          A       -20
  2          A2       350
  3          X        40
  4          A        50
  5          A        -10
  6          A2       10

应该生成:

itemorder   name    qty       modifyed_sum
  1          A       -20          20       / 40 + (-20)
  2          A2       350         40       / not A
  3          X        40           40       / encounter X, restart sum with X qty.
  4          A        50          140       / 90 + 50
  5          A        -10         90        / 100 +  (-10)
  6          A2       10          100       / not A

我使用这个查询来求和:

SELECT 100 + Sum(CASE WHEN name = 'a' THEN qty ELSE 0 END)OVER(ORDER BY itemorder DESC) as modifyed_sum,
       qty,
       name,
       itemorder
FROM   Table_Name
ORDER  BY itemorder ASC

如何修改它以处理 X 大小写？ (可以有多个X)

Answer 1

你需要一个 RECURSIVE 查询

SQL FIDDLE DEMO

WITH RECURSIVE t("itemorder", "name", "qty", "modifyed_sum", "level") AS (
    SELECT "itemorder", 
           "name", 
           "qty", 
           100 +  CASE 
                     WHEN "name" = 'A' THEN "qty"
                     ELSE 0
                  END as "modifyed_sum",
           "itemorder" as "level"
     FROM myTable
     WHERE "itemorder" = (SELECT max("itemorder") FROM myTable)
     UNION ALL
     SELECT myTable."itemorder", 
            myTable."name", 
            myTable."qty", 
            CASE 
                WHEN myTable."name" = 'A' THEN t."modifyed_sum" + myTable."qty"
                WHEN myTable."name" = 'X' THEN myTable."qty"
                ELSE t."modifyed_sum"          
            END as "modifyed_sum",
           myTable."itemorder" as "level"
     FROM myTable 
     JOIN t
       ON myTable."itemorder" + 1 = t."itemorder" 
      AND myTable."itemorder" = t."level" - 1
     WHERE  myTable."itemorder" > 0        
)
SELECT *
FROM t
ORDER BY "itemorder"

输出

| itemorder | name | qty | modifyed_sum | level |
|-----------|------|-----|--------------|-------|
|         1 |    A | -20 |           20 |     1 |
|         2 |   A2 | 350 |           40 |     2 |
|         3 |    X |  40 |           40 |     3 |
|         4 |    A |  50 |          140 |     4 |
|         5 |    A | -10 |           90 |     5 |
|         6 |   A2 |  10 |          100 |     6 |