Subtitute Parts/Rows Postgresql - sql

Question

I want to create relationship in Postgresql that allows me to have ‘substitute’ parts. For example, parts with id 1, 2 and 4 are substitutes.
One way to do this would be to setup a sub_id field and fill that with the substitute part’s id. But as you can see from the dataset below, a simple query:
SELECT *
FROM part
WHERE sub_id = 1
would not return all the substitute parts for part AA (part A2 would be missed). How can I ensure all the substitute parts are catered for?
I know that if the sub_id was 1 for part A2, all would be good. However, it’s possible that in real world usage the users end up making a mistake and that would return the wrong result.
id part sub_id
1 AA 1
2 A 1
3 B NULL
4 A2 2

Answer 1

You can try a different approach.
I don't know what your needs are but this is a general idea:
Set up a table that define a part "group":
partgid, part type, partg name
1 A Engine for A319
2 B Wheel for A319
code:
Create Table partgroup
(
partgid int,
parttype text,
partgname text
);
then define parts in the group:
partid partgid partname manufacturerid
12 1 Engine X319 800
13 1 Engine XL319 800
14 1 Engine XFR319 784
15 2 Wheel F1111 341
code:
Create Table parts
(
partid int,
partgid int,
partname text,
manufacturerid int
);
then you can access all parts in a specific group in a simple query:
By ID:
select *
from parts
where partgid='ID'
By name:
select *
from parts
left join partgroup on (partgroup.partgid=parts.partgid)
where partgroup.parttype= 'TYPE NAME'