How to take the smallest date of a group? - sql

Question

I have a dataset which looks like that:
| id | status | open_date | name |
| 8 | active | 2019-3-2 | blab |
| 8 | active | 2019-3-8 | blub |
| 8 | inactive | 2019-3-9 | hans |
| 8 | active | 2019-3-10 | ana |
| 9 | active | 2019-3-4 | mars |
I want to achieve the following:
| id | status | open_date | name | status_change_date |
| 8 | active | 2019-3-2 | blab | 2019-3-2
| 8 | active | 2019-3-8 | blub | 2019-3-2
| 8 | inactive | 2019-3-9 | Hans | 2019-3-9
| 8 | active | 2019-3-10 | ana | 2019-3-10
| 9 | active | 2019-3-4 | mars | 2019-3-4
for each id I like to calculate when the status has last changed
I already tried with groupBy, but the problem is I only want to group by the rows with Active and Inactive which are next to each other. If there is an INACTIVE between ACTIVE I like to make a new group for the new ACTIVE.
Someone has an idea to solve that?

Answer 1

Here is a pure SQL solution that uses window functions. This works by generating a partition that contains consecutive records that have the same id and status.
SELECT
id,
status,
open_date,
name,
MIN(open_date) OVER(PARTITION BY id, rn1 - rn2 ORDER BY open_date) status_change_date
FROM (
SELECT
t.*,
ROW_NUMBER() OVER(PARTITION BY id ORDER BY open_date) rn1,
ROW_NUMBER() OVER(PARTITION BY id, status ORDER BY open_date) rn2
FROM mytable t
) x
ORDER BY id, open_date
Demo on DB Fiddle:
| id | status | open_date | name | status_change_date |
| --- | -------- | ---------- | ---- | ------------------ |
| 8 | active | 2019-03-02 | blab | 2019-03-02 |
| 8 | active | 2019-03-08 | blub | 2019-03-02 |
| 8 | inactive | 2019-03-09 | hans | 2019-03-09 |
| 8 | active | 2019-03-10 | ana | 2019-03-10 |
| 9 | active | 2019-03-04 | mars | 2019-03-04 |

Answer 2

Thats the answer on How to take the smallest date of a group?
let minDate = new Date('0001-01-01T00:00:00Z');
dataset.forEach(x => if( x.date > this.minDate) { this.minDate = x.date } )
console.log(this.minDate);

Answer 3

You can try this:
var movies = [
{title: 'The Godfather', rating: 9.2, release: '24 March 1972'},
{title: 'The Godfather: Part II', rating: 9.0, release: '20 December 1972'},
{title: 'The Shawshank Redemption', rating: 9.3, release: '14 October 1994'},
];
movies.sort(function(a, b) {
var dateA = new Date(a.release), dateB = new Date(b.release);
return dateA - dateB;
});
This sortby works because js lets you compare arithmetic on date objects, which are automatically converted to numeric representations first.
In SQL use MIN function:
ORDER
Id
OrderDate
OrderNumber
CustomerId
TotalAmount
SELECT MIN(OrderDate)
FROM [Order]
WHERE YEAR(OrderDate) = 2013