Question

我有桌子

CREATE TABLE t1
(
  id           serial           NOT NULL,
  in_quantity  bigint           NULL,
  price        money            NOT NULL,
  out_quantity bigint           NULL,
  stamp        timestamp        NOT NULL
);

有这样的数据，例如（日期相同，但不是时间）

INSERT INTO t1 (in_quantity, price, out_quantity, stamp)
VALUES
( 100, 10.00, NULL, '2014-10-20 00:00:00'), -- id =  1
( 200, 11.00, NULL, '2014-10-20 00:01:00'), -- id =  2
( 300, 12.00, NULL, '2014-10-20 00:02:00'), -- id =  3
(NULL, 13.00,  400, '2014-10-20 00:03:00'), -- id =  4
(NULL, 14.00,  500, '2014-10-20 00:04:00'), -- id =  5

( 600, 15.00, NULL, '2014-10-20 00:15:00'), -- id =  6
( 700, 16.00, NULL, '2014-10-20 00:16:00'), -- id =  7
( 800, 17.00, NULL, '2014-10-20 00:17:00'), -- id =  8
(NULL, 18.00,  900, '2014-10-20 00:18:00'), -- id =  9
(NULL, 19.00, 1000, '2014-10-20 00:19:00'), -- id = 10

(2300, 23.00, NULL, '2014-10-20 00:23:00'), -- id = 11
(2400, 24.00, NULL, '2014-10-20 00:24:00'); -- id = 12

我需要从此表中获取行，其中包含特定集合中每个日期范围的最大输入和输出数量。例如：

( "2014-10-20 00:00:00" : "2014-10-20 00:05:00" ]
( "2014-10-20 00:05:00" : "2014-10-20 00:10:00" ]
( "2014-10-20 00:10:00" : "2014-10-20 00:15:00" ]
( "2014-10-20 00:15:00" : "2014-10-20 00:20:00" ]
( "2014-10-20 00:20:00" : "2014-10-20 00:25:00" ]

这个例子我想要的结果是

interval begin        | interval end          | max_in_q | max_in_q_id | max_out_q | max_out_q_id 
======================+=======================+==========+=============+===========+=============
"2014-10-20 00:00:00" | "2014-10-20 00:05:00" | 300      | 3           | 400       | 4
"2014-10-20 00:05:00" | "2014-10-20 00:10:00" | NULL     | NULL        | NULL      | NULL        
"2014-10-20 00:10:00" | "2014-10-20 00:15:00" | NULL     | NULL        | NULL      | NULL        
"2014-10-20 00:15:00" | "2014-10-20 00:20:00" | 800      | 8           | 1000      | 10
"2014-10-20 00:20:00" | "2014-10-20 00:25:00" | 2400     | 12          | NULL      | NULL

因此。我可以使用像这样的查询生成类似的集合

SELECT
   i::timestamp AS dleft,
   i::timestamp + '1 hour' AS dright 
FROM
   generate_series('2014-10-20 00:00:00'::timestamp, '2014-10-20 23:00:00'::timestamp, '1 hour') AS i

但是我无法想象如何为这些小范围中的每一个运行聚合函数以及如何加入结果。

Answer 1

首先，您需要意识到，在任何RDBMS中，每个聚合值都需要id s，这不是一个简单的查询。

这个问题主要通过PostgreSQL中的DISTINCT ON来解决：

SELECT DISTINCT ON (s)
  s ts_start, s + '5 minutes' ts_end, in_quantity max_in_q, id max_in_id
FROM
  generate_series('2014-10-20 00:00:00'::timestamp, '2014-10-20 00:20:00'::timestamp, '5 minutes') s
LEFT JOIN
  t1 ON stamp <@ tsrange(s, s + '5 minutes', '(]')
ORDER BY
  s, in_quantity DESC NULLS LAST;

但这只允许你选择一个最大/最小值，以及它们所属的整行。

如果你真的需要两个最大列，你需要编写自联接和子查询，这不会那么快：

SELECT
  lower(r) ts_start, upper(r) ts_end, max_in_q, max_in.id max_in_id, max_out_q, max_out.id max_out_id
FROM (
  SELECT
    r, max(in_quantity) max_in_q, max(out_quantity) max_out_q
  FROM
    generate_series('2014-10-20 00:00:00'::timestamp, '2014-10-20 00:20:00'::timestamp, '5 minutes') s,
    tsrange(s, s + '5 minutes', '(]') r
  LEFT JOIN
    t1 ON stamp <@ r
  GROUP BY
    r
  ORDER BY
    r
) m
LEFT JOIN
  t1 max_in ON max_in.in_quantity = max_in_q
LEFT JOIN
  t1 max_out ON max_out.out_quantity = max_out_q;

注意：对于第二个版本，您需要自己处理重复项，因为in_quantity和out_quantity并不是唯一的。

SQLFiddle

Answer 2

我认为在range type：

的帮助下，这可能非常简单

WITH data(in_quantity,price,out_quantity,stamp) AS (VALUES
( 100::int8, 10.00, NULL::int8, '2014-10-20 00:00:00'::timestamp), -- id =  1
( 200, 11.00, NULL, '2014-10-20 00:01:00'), -- id =  2
( 300, 12.00, NULL, '2014-10-20 00:02:00'), -- id =  3
(NULL, 13.00,  400, '2014-10-20 00:03:00'), -- id =  4
(NULL, 14.00,  500, '2014-10-20 00:04:00'), -- id =  5

( 600, 15.00, NULL, '2014-10-20 00:15:00'), -- id =  6
( 700, 16.00, NULL, '2014-10-20 00:16:00'), -- id =  7
( 800, 17.00, NULL, '2014-10-20 00:17:00'), -- id =  8
(NULL, 18.00,  900, '2014-10-20 00:18:00'), -- id =  9
(NULL, 19.00, 1000, '2014-10-20 00:19:00'), -- id = 10

(2300, 23.00, NULL, '2014-10-20 00:23:00'), -- id = 11
(2400, 24.00, NULL, '2014-10-20 00:24:00')
)
SELECT
   tsrange(i,i+INTERVAL '1h','[)') r,
   max(in_quantity)                max_in_q,
   max(out_quantity)               max_out_q
  FROM generate_series('2014-10-20 00:00:00'::timestamp,
                       '2014-10-20 23:00:00'::timestamp, '1 hour') AS i
  LEFT JOIN data d ON tsrange(i,i+INTERVAL '1h','[)') @> d.stamp
 GROUP BY r
 ORDER BY r;

检查SQL Fiddle

我在这里使用了LEFT JOIN因为我认为您希望看到所有范围，以满足您的需求。

postgresql：聚合一组日期范围内的数据

2 个答案: