0

The data I got is

id date cnt
1 '2021-11-26' 1
1 '2021-11-25' 1
1 '2021-11-24' 1
1 '2021-11-23' 1

The result I want is

id from_date to_date cnt
1 '2021-11-23' '2021-11-24' 2
1 '2021-11-23' '2021-11-25' 3
1 '2021-11-23' '2021-11-26' 4
1 '2021-11-24' '2021-11-25' 2
1 '2021-11-24' '2021-11-26' 3
1 '2021-11-25' '2021-11-26' 2

Is there a way to generate those dates (from_date, to_date) from the date column in the data?

Do I need to use loop from the iteration of the date?

What else I can think of to get close to the result?

Thanks in advance

2

Is there a way to generate those dates (from_date, to_date)

A "triangular join":

SELECT a.date AS from_date,
       z.date AS to_date
    FROM t AS a
    CROSS JOIN t AS z
    WHERE a.date < z.date

That can then be joined again to t to deal with the sums.

4
  • That's more of a triangular join. You may as well use proper join syntax with an ON clause Nov 28 '21 at 10:38
  • Hmmm... I learned something new. MySQL never mentions "triangular joins".
    – Rick James
    Nov 28 '21 at 17:18
  • No it wouldn't there is no special syntax, just JOIN t AS z ON a.date < z.date Nov 28 '21 at 17:40
  • You saved my days! Thanks a lot!
    – Eric Lee
    Nov 29 '21 at 3:31
0

Assuming a simple table structure like this:

CREATE TABLE IF NOT EXISTS `Sample` (
    `id`            int(11)        UNSIGNED   NOT NULL    AUTO_INCREMENT,
    `date`          timestamp                 NOT NULL    ,
    `cnt`           int(11)        UNSIGNED   NOT NULL    DEFAULT 1,
    PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

With data like this:

INSERT INTO `Sample` (`date`)
VALUES ('2021-11-26'),
       ('2021-11-25'),
       ('2021-11-24'),
       ('2021-11-23');

You can do this:

SELECT tmp.`id`,
       DATE_FORMAT(tmp.`from_dts`, '%Y-%m-%d') as `from_date`,
       DATE_FORMAT(tmp.`to_dts`, '%Y-%m-%d') as `to_date`,
       SUM(sm.`cnt`) as `cnt`
  FROM `Sample` sm INNER JOIN (SELECT a.`id`, DATE_FORMAT(a.`date`, '%Y-%m-%d 00:00:00') as `from_dts`, DATE_FORMAT(z.`date`, '%Y-%m-%d 23:59:59') as `to_dts`
                                 FROM `Sample` a INNER JOIN `Sample` z ON a.`date` < z.`date`) tmp ON sm.`date` BETWEEN tmp.`from_dts` AND tmp.`to_dts`
 GROUP BY tmp.`id`, `from_date`, `to_date`
 ORDER BY `from_date`, `to_date`;

There are certainly other ways to accomplish this same goal but, this will do in a pinch. If you are going to be running this sort of query against millions of records, though, you will want to approach the problem very differently.

1
  • Somehow the summed cnt shows more than I expected. but the range of the date were generated correctly.
    – Eric Lee
    Nov 29 '21 at 3:32

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