问题
I have the following issue:
I have this entity, let's call it ENTITY_THREE, which is part of a arc barred relationship:
Three entities ENTITY_ONE, ENTITY_TWO and ENTITY_THREE which are part of an arc barred relationship
Please note that ENTITY_THREE has a composite primary key: ID, ID_OF_ONE, ID_OF_TWO and ENTITY_TWO has a composite primary key as well: ID, ID_OF_ONE.
Now, according to the description of the assignment, if ENTITY_TWO has more than 1 of ENTITY_THREE, ENTITY_THREE needs to be numbered by ENTITY_TWO, like so:
ENTITY TWO:
ID
1
2
ENTITY THREE:
ID ID_OF_TWO
1 1
2 1
3 1
1 2
2 2
3 2
So, what I basically want is that when you use an INSERT statement, you must not provide the ID: it adds it for you automatically. But the ID is numbered by a foreign key: all records with an ID_OF_TWO 1, let's say 5, will be numbered 1 through 5, all records with an ID_OF_TWO 2, let's say 3, will be numbered 1 through 3, and so on …
Is there any way (a TRIGGER maybe?) I can accomplish this?
@EDIT:
Earlier on I talked about an arc relationship, but what I actually mean't was a barred relationship, my bad.
@Update:
I saw something a couple of days ago that might work, but I'm not too sure. I'm going to try it anyways. I will let you guys know if it worked or not …
来源：https://stackoverflow.com/questions/50486727/data-model-primary-key-numbering-issue