sql query for diff between rows - mysql

Question

I have a table having dates in it, I would want to subtract the first date with the second, the second with the third and so on till the last n-1 with n.
How do I write a query for this?
The table would is called Random and the column name is date
date
+------------+
| 2009-06-20 |
| 2010-02-12 |
| 2012-03-14 |
| 2013-09-10 |
| 2014-01-01 |
| 2015-04-10 |
| 2015-05-01 |
| 2016-01-01 |
+------------+

Answer 1

You need to get the next date. I would use a correlated subquery:
select t.date,
(select min(t2.date)
from t t2
where t2.date > t.date
) as next_date
from t;
You just need to use datediff() to get the difference in days.

Answer 2

Use ROW_NUMBER
For line numbering and then use a sub query to calculate the difference
SELECT column_date
,DATEDIFF( D , column_date
,(SELECT column_date FROM
(
SELECT column_date , ROW_NUMBER() OVER ( ORDER BY column_date) AS RowMum
FROM table_Random AS tBL_1
) AS tbl_2
WHERE tbl_2.RowMum= tBL_1.RowMum-1
)
) DIFF
FROM
(
SELECT column_date , ROW_NUMBER() OVER ( ORDER BY column_date) AS RowMum
FROM table_Random
) AS tBL_1

Answer 3

I did not notice the mysql tag when I wrote my answer first so am updating it now with link to MySQL 8.0 fiddle
https://www.db-fiddle.com/f/myUJYeFrMXmU1piQXAmnv4/0
/* tested against MySQL v8.0 */
WITH T(d) AS (
SELECT '2009-06-20' as d
UNION
SELECT '2010-02-12'
UNION
SELECT '2012-03-14'
UNION
SELECT '2013-09-10'
UNION
SELECT '2014-01-01'
UNION
SELECT '2015-04-10'
UNION
SELECT '2015-05-01'
UNION
SELECT '2016-01-01'
), LAGGED(d, next_d) AS (
SELECT d, LEAD(d) OVER (ORDER BY d ASC) AS next_d
FROM T
)
/* datediff args are in opposite order to SQL server. Also,
only day part is considered */
SELECT l.d, l.next_d, DATEDIFF(l.next_d, l.d) AS n_days
FROM LAGGED AS l
Here is my original answer that targeted SQL Server:
WITH T(d) AS (
SELECT d FROM (
VALUES
('2009-06-20'),
('2010-02-12'),
('2012-03-14'),
('2013-09-10'),
('2014-01-01'),
('2015-04-10'),
('2015-05-01'),
('2016-01-01')
) AS T1(d)
), LAGGED(d, next_d) AS (
SELECT d, LEAD(d) OVER (ORDER BY d ASC) AS next_d
FROM T
)
SELECT l.d, l.next_d, DATEDIFF(DAY, l.d, l.next_d) AS n_days
FROM LAGGED AS l
and produces this output (modulo the fussy hand-editing I have done):
d next_d n_days
2009-06-20 2010-02-12 237
2010-02-12 2012-03-14 761
2012-03-14 2013-09-10 545
2013-09-10 2014-01-01 113
2014-01-01 2015-04-10 464
2015-04-10 2015-05-01 21
2015-05-01 2016-01-01 245
2016-01-01 NULL NULL