sql - 按给定数量的行值分组

Question

我在第 1 列中有一个值列表，现在我想获得下一个 5 行值或 6 个行值的总和，如下所示，并将值填充到适当的列中。

例如，如果您看到“next-5row-value”列的第一行值将是从当前行到接下来 5 行的值的总和，即 9，下一列将是接下来 5 行值的总和那个参考点。

我正在尝试编写函数来循环得出总和。有没有有效的方法。有人可以帮我吗。我正在使用 postgres，greenplum。谢谢！

Answer 1

例如，如果你有这个简单的表：

sebpa=# \d numbers
                         Table "public.numbers"
 Column |  Type   |                      Modifiers
--------+---------+------------------------------------------------------
 id     | integer | not null default nextval('numbers_id_seq'::regclass)
 i      | integer |

sebpa=# select * from numbers limit 15;
  id  | i
------+---
 3001 | 3
 3002 | 0
 3003 | 5
 3004 | 1
 3005 | 1
 3006 | 4
 3007 | 1
 3008 | 1
 3009 | 4
 3010 | 0
 3011 | 4
 3012 | 0
 3013 | 3
 3014 | 2
 3015 | 1
(15 rows)

你可以使用这个 sql：

sebpa=# select id, i, sum(i) over( order by id rows between 0 preceding and 4 following) from numbers;
  id  | i | sum
------+---+-----
 3001 | 3 |  10
 3002 | 0 |  11
 3003 | 5 |  12
 3004 | 1 |   8
 3005 | 1 |  11
 3006 | 4 |  10
 3007 | 1 |  10
 3008 | 1 |   9
 3009 | 4 |  11
 3010 | 0 |   9
 3011 | 4 |  10
 3012 | 0 |  10
 3013 | 3 |  13
 3014 | 2 |  15
 3015 | 1 |  17
 3016 | 4 |  20
 3017 | 3 |  17
--cutted output

Answer 2

你可以尝试这样的事情：

SELECT V,
       SUM(V) OVER(ORDER BY YourOrderingField
                       ROWS BETWEEN 1 FOLLOWING AND 5 FOLLOWING) AS next_5row_value,
       SUM(V) OVER(ORDER BY YourOrderingField
                       ROWS BETWEEN 1 FOLLOWING AND 6 FOLLOWING) AS next_6row_value
FROM YourTable;

如果您不想在“next_5row_value”列（第 6 行相同）中出现 NULL，则可以使用返回第一个非空表达式的 COALESCE 函数（PostgreSQL 也支持）。像这样的东西：

SELECT V,
       COALESCE(SUM(V) OVER(ORDER BY YourOrderingField
                            ROWS BETWEEN 1 FOLLOWING AND 5 FOLLOWING), 0) AS next_5row_value,
       COALESCE(SUM(V) OVER(ORDER BY YourOrderingField
                            ROWS BETWEEN 1 FOLLOWING AND 6 FOLLOWING), 0) AS next_6row_value
FROM YourTable;

Answer 3

我不认为 Postgres 8.4 支持窗口框架的全部功能。您可以使用以下方法执行此操作lead()：

select value,
       (value +
        lead(value, 1) over (order by id) +
        lead(value, 2) over (order by id) +
        lead(value, 3) over (order by id) +
        lead(value, 4) over (order by id)
       ) as next5,
       (value +
        lead(value, 1) over (order by id) +
        lead(value, 2) over (order by id) +
        lead(value, 3) over (order by id) +
        lead(value, 4) over (order by id) +
        lead(value, 5) over (order by id)
       ) as next5
from table t;

如果数据库支持，使用窗框定义绝对是更好的方法。但是上面的方法也可以。