SQL value of previous (unknown) date

Question

I have a table with articles, Day Date, and amount of bought. I want a reslut table where I can see the amount off all Articles and how many where bought and the amount they where bought at the unknown date before:

Example result of:

select articleid, amount, date from table1 where articleid in(7,8)

|------------|---------|----------|
| articleid  | amount  |   date   |
|------------|---------|----------|
|    7       |    34   |20.10.2019|
|------------|---------|----------|
|    7       |    2    |15.10.2019|
|------------|---------|----------|
|    8       |    12   |13.10.2019|
|------------|---------|----------|
|    8       |    35   |15.09.2019|
|------------|---------|----------|

The result should look like:

|------------|---------|----------|----------|----------|
| articleid  | amount  |   date   |prev date |prevamount|
|------------|---------|----------|----------|----------|
|    7       |    34   |20.10.2019|15.10.2019|     2    |
|------------|---------|----------|----------|----------|
|    7       |    2    |15.10.2019|          |          |
|------------|---------|----------|----------|----------|
|    8       |    12   |13.10.2019|15.09.2019|     35   |
|------------|---------|----------|----------|----------|
|    8       |    35   |15.09.2019|          |          |
|------------|---------|----------|----------|----------|

Is this anyway possibile to do?

Best Zio

Answer 1

You want lag() :

select 
    articleid, 
    amount,
    date,
    lag(date) over(partition by articleid order by date) prevdate,
    lag(amount) over(partition by articleid order by date) prevamount
from table1
order by articleid, date desc