Question

Just beginning to learn about SQL and had a question I couldn’t figure out.

I have a setup based on the following tables and their primary keys, the columns with the same name between tables are constrained by foreign keys:

Company:

• CompanyId

Division:

• CompanyId
• DivisionId

Resource:

• CompanyId
• ResourceId

DivisionResource :

• CompanyId
• DivisionId
• ResourceId

• DivisionResource is used to create a many to many relation between division and resource and constrain them so that divisions can only be linked to resources of the same company.
• Without the DivisionResource, Division and Resource wouldn’t need the CompanyId as a primary key to contain unique records.

So my question is this: Is there a way to create a similar constraint as DivisionResource creates without forcing Division and Resource to have an extra column in its primary key?

Answer 1

ResourceCompany and DivisionCompany in the schema below are connecting tables. They will have CompanyId in their primary key but Resource and Division will have primary keys with one column. This is what you looked for.

Resource -> ResourceCompany

DivisionResource -> ResourceCompany

Division -> DivisionCompany

DivisionResource -> DivisionCompany

create table Company (CompanyId int primary key);

create table DivisionCompany (
    CompanyId int foreign key references Company(CompanyId), 
    DivisionId int, 
    constraint pk_div_company primary key (DivisionId, CompanyId)
    );

create table Division (
    DivisionId int primary key,
    CompanyId int,
    constraint fk_div_company foreign key (DivisionId, CompanyId) references DivisionCompany(DivisionId, CompanyId));

create table ResourceCompany (
    CompanyId int foreign key references Company(CompanyId), 
    ResourceId int, 
    constraint pk_res primary key (ResourceId, CompanyId));

create table Resource(
    ResourceId int primary key,
    CompanyId int, 
    constraint fk_res_company foreign key (ResourceId, CompanyId) references ResourceCompany(ResourceId, CompanyId)
    );

create table DivisionResource(
    CompanyId int,
    DivisionId int, 
    ResourceId int,
    constraint pk_DivRes primary key (DivisionId, ResourceId),
    constraint fk_DivCompany foreign key (DivisionId, CompanyId) references DivisionCompany(DivisionId, CompanyId),
    constraint fk_ResCompany foreign key (ResourceId, CompanyId) references ResourceCompany(ResourceId, CompanyId)
    );