一张表的累计金额

Question

在 Postgres 中对表执行累积求和的最佳方法是什么，以便在向表中添加更多字段/列的情况下带来最佳性能和灵活性。

表格

a b d 1 59 15 181 2 16 268 3 219 4 102

累积

a b d 1 59 15 181 2 31 449 3 668 4 770

Answer 1

您可以使用窗口函数，但您需要额外的逻辑来避免存在NULLs 的值：

SELECT id,
       (case when a is not null then sum(a) OVER (ORDER BY id) end) as a,
       (case when b is not null then sum(b) OVER (ORDER BY id) end) as b,
       (case when d is not null then sum(d) OVER (ORDER BY id) end) as d 
FROM table;

这假定指定排序的第一列称为id。

Answer 2

运行求和的窗口函数。

SELECT sum(a) OVER (ORDER BY d) as "a",
       sum(b) OVER (ORDER BY d) as "b",
       sum(d) OVER (ORDER BY d) as "d" 
FROM table;

如果您有多个运行总和，请确保订单相同。

• http://www.postgresql.org/docs/8.4/static/tutorial-window.html
• http://www.postgresonline.com/journal/archives/119-Running-totals-and-sums-using-PostgreSQL-8.4-Windowing-functions.html

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请务必注意，如果您希望您的列在您的问题中显示为汇总表（每个字段唯一排序），则需要更多的参与。

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更新：我已修改查询以进行所需的排序，但没有给定的公共字段。

SQL 小提琴：(1) Only Aggregates，或(2) Source Data Beside Running Sum

WITH 
rcd AS ( 
  select row_number() OVER() as num,a,b,d 
  from tbl
),
sorted_a AS (
  select row_number() OVER(w1) as num, sum(a) over(w2) a
  from tbl
  window w1 as (order by a nulls last),
         w2 as (order by a nulls first)
),
sorted_b AS (
  select row_number() OVER(w1) as num, sum(b) over(w2) b
  from tbl
  window w1 as (order by b nulls last),
         w2 as (order by b nulls first)
),
sorted_d AS (
  select row_number() OVER(w1) as num, sum(d) over(w2) d
  from tbl
  window w1 as (order by d nulls last),
         w2 as (order by d nulls first)
)

SELECT sorted_a.a, sorted_b.b, sorted_d.d 
FROM rcd 
JOIN sorted_a USING(num)
JOIN sorted_b USING(num)
JOIN sorted_d USING(num)
ORDER BY num;

Answer 3

我认为你真正想要的是：

SELECT id
     , sum(a) OVER (PARTITION BY a_grp ORDER BY id) as a
     , sum(b) OVER (PARTITION BY b_grp ORDER BY id) as b
     , sum(d) OVER (PARTITION BY d_grp ORDER BY id) as d 
FROM  (
   SELECT *
        , count(a IS NULL OR NULL) OVER (ORDER BY id) as a_grp
        , count(b IS NULL OR NULL) OVER (ORDER BY id) as b_grp
        , count(d IS NULL OR NULL) OVER (ORDER BY id) as d_grp
   FROM   tbl
   ) sub
ORDER  BY id;

表达式count(col IS NULL OR NULL) OVER (ORDER BY id) 在子查询sub 中形成a、b 和d 的连续非空行组。

在外部查询中，我们运行每组的累积总和。 NULL 值形成自己的组并自动保留NULL。无需额外的CASE 声明。

SQL Fiddle（为列a添加了一些值来演示效果）。