Selecting the first instance of a vendor, part combination - sql

Question

I am trying to create an indicator for if a particular transaction was the first time a part was purchased from a particular vendor.
I have a dataset that looks like this:
| transaction_id | vendor_id | part_id | trans_date |
|:--------------:|:---------:|:-------:|:-----------------:|
| 9Bx*2Pc' | a | 873 | 10/12/2018 |
| 1Po.4Ot, | a | 473 | 4/22/2016 |
| 9Sk"7Kv/ | b | 123 | 7/23/2016 |
| 2Lz&7Hu& | a | 873 | 12/20/2017 |
| 8Lz)5Is# | b | 743 | 10/22/2016 |
| 5Sc'6Jl/ | a | 113 | 10/6/2016 |
| 0Ra&8Hb& | a | 653 | 10/4/2017 |
| 4Wc-8Of* | c | 333 | 8/3/2017 |
| 8Vv+9Yo/ | c | 333 | 12/7/2016 |
| 6Qh!1Ha- | c | 333 | 3/28/2017 |
| 2Ol%4Rs# | c | 333 | 5/2/2017 |
| 1Gg#8Cm% | c | 333 | 11/15/2016 |
| 0Lw(6Pv/ | d | 873 | 8/13/2017 |
| 1Gy/7Zw, | a | 443 | 10/12/2018 |
| 2Gz,4Gp. | b | 103 | 1/5/2018 |
| 5Dj)6Wc+ | a | 893 | 12/17/2016 |
| 5Hl-8Ds! | a | 903 | 12/8/2017 |
| 8Ws$3Vy* | b | 873 | 1/13/2018 |
What I am looking to do is determine if the transaction_id was the first time (sorted by trans_date), that the part_id was purchased from a vendor_id. I would imagine the ideal output to look like this:
| transaction_id | vendor_id | part_id | trans_date | first_time |
|:--------------:|:---------:|:-------:|:-----------------:|:----------:|
| 9Bx*2Pc' | a | 873 | 10/12/2018 | N |
| 1Po.4Ot, | a | 473 | 4/22/2016 | Y |
| 9Sk"7Kv/ | b | 123 | 7/23/2016 | Y |
| 2Lz&7Hu& | a | 873 | 12/20/2017 | Y |
| 8Lz)5Is# | b | 743 | 10/22/2016 | Y |
| 5Sc'6Jl/ | a | 113 | 10/6/2016 | Y |
| 0Ra&8Hb& | a | 653 | 10/4/2017 | Y |
| 4Wc-8Of* | c | 333 | 8/3/2017 | N |
| 8Vv+9Yo/ | c | 333 | 12/7/2016 | N |
| 6Qh!1Ha- | c | 333 | 3/28/2017 | N |
| 2Ol%4Rs# | c | 333 | 5/2/2017 | N |
| 1Gg#8Cm% | c | 333 | 11/15/2016 | Y |
| 0Lw(6Pv/ | d | 873 | 8/13/2017 | Y |
| 1Gy/7Zw, | a | 443 | 10/12/2018 | Y |
| 2Gz,4Gp. | b | 103 | 1/5/2018 | Y |
| 5Dj)6Wc+ | a | 893 | 12/17/2016 | Y |
| 5Hl-8Ds! | a | 903 | 12/8/2017 | Y |
| 8Ws$3Vy* | b | 873 | 1/13/2018 | Y |
So far, I have tried (which was influenced by this post):
WITH
first_instance AS (
SELECT
tbl_trans.*,
ROW_NUMBER() OVER (PARTITION BY vendor_id||part_id ORDER BY trans_date) AS row_nums
FROM
tbl_trans
)
SELECT
x.*,
CASE WHEN y.row_nums = 1 THEN 'Y' ELSE 'N' END AS first_time_indicator
FROM
tbl_trans x
LEFT JOIN first_instance y
But I am met with:
ORA-00905: missing keyword
I have created a SQL FIDDLE with this data and the query thus far for testing. How can I determine the if a transaction was a first time purchase for a part/vendor combination?

Answer 1

Use window functions:
select t.*,
(case when row_number() over (partition by vendor_id, part_id order by trans_date) = 1
then 'Y' else 'N'
end) as first_time
from tbl_trans t;
You don't need a join.

Answer 2

Apart from row_number, there are multiple ways of achieving the desired result using analytical function as follows.
You can use first_value analytical function as follows:
Select t.*,
Case
when first_value(trans_date)
over (partition by vendor_id, part_id order by trans_date) = trans_date
then 'Y'
else 'N'
end as first_time
From your_table t;
The same way, you can also use min as follows:
Select t.*,
Case
when min(trans_date)
over (partition by vendor_id, part_id) = trans_date
then 'Y'
else 'N'
end as first_time
From your_table t;