Days diff based on selected date from succeeding row - mysql

Question

How can I get the succeeding or previous data row result from a query, as I wanted to compute days difference based on date_created for succeeding rows?
SELECT
-- *,
h.date_created,
-- (select date_created where id = h.id and pci_s = h.pci_s + 1) as dc,
h.id,
h.date_created,
CONCAT('B', h.pci_b) AS batch,
h.pci_s,
DATEDIFF(h.date_created, h.date_created) as days_in_stage
FROM
historical h
WHERE
h.pci_b = 1
;
Expected
date_created id date_created batch pci_s days_in_stage
2021-07-18T06:32:26Z 1 2021-07-18T06:32:26Z B1 0 0
2021-07-20T06:32:26Z 4 2021-07-20T06:32:26Z B1 1 2
Here's the jsfiddle
http://sqlfiddle.com/#!9/f32a242/3
Currently using: Mysql 5.7.33

Answer 1

I get the succeeding or previous data row result
that you are looking for LEAD or LAG window function.
but your MySQL version is lower than 8.0 which didn't support window function.
you can try to use a subquery to make LEAD or LAG window function.
Query 1:
SELECT
h.date_created,
h.id,
h.date_created,
CONCAT('B', h.pci_b) AS batch,
h.pci_s,
COALESCE(DATEDIFF(h.date_created,(
SELECT hh.date_created
FROM historical hh
WHERE h.pci_b = hh.pci_b AND h.date_created > hh.date_created
ORDER BY hh.date_created DESC
LIMIT 1
)),0) as days_in_stage
FROM
historical h
WHERE
h.pci_b = 1
Results:
| date_created | id | date_created | batch | pci_s | days_in_stage |
|----------------------|----|----------------------|-------|-------|---------------|
| 2021-07-18T06:32:26Z | 1 | 2021-07-18T06:32:26Z | B1 | 0 | 0 |
| 2021-07-20T06:32:26Z | 4 | 2021-07-20T06:32:26Z | B1 | 1 | 2 |

Answer 2

With MySQL8 you can simply use LAG() or LEAD() window functions.
https://dev.mysql.com/doc/refman/8.0/en/window-function-descriptions.html#function_lag
With MySQL5.x you don't have that so can instead use correlated-sub-queries, for example...
SELECT
-- *,
(SELECT date_created FROM historical WHERE date_created < h.date_created ORDER BY date_Created DESC LIMIT 1) AS prev_date_created,
-- (select date_created where id = h.id and pci_s = h.pci_s + 1) as dc,
h.id,
h.date_created,
CONCAT('B', h.pci_b) AS batch,
h.pci_s,
DATEDIFF(h.date_created, h.date_created) as days_in_stage
FROM
historical h
WHERE
h.pci_b = 1
ORDER BY
h.date_created
;
https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=0ce3b601688e1de11eda1007bffea9f9

Answer 3

In the new version of mysql you can use Lead and Lag functions for getting next row and previous row data. But if you are not using current version then this will not work, there is other solution.
Please share your mysql version if not using new version.
For eg for new version:
SELECT
-- *,
h.date_created,
-- (select date_created where id = h.id and pci_s = h.pci_s + 1) as dc,
h.id,
h.date_created,
CONCAT('B', h.pci_b) AS batch,
h.pci_s,
DATEDIFF(h.date_created, h.date_created) as days_in_stage,
lead(h.date_created)over (order by h.date_created) next_row_date,
lag(h.date_created)over (order by h.date_created) pre_row_date
FROM
historical h
WHERE
h.pci_b = 1
;