How would I associate users with different company tables? - postgresql

Question

In the below diagram you can see I have profiles for users. A user means the profile is associated with a login. If they don't have a login account they are merely a "contact" at the company tables you see on the right.
I am creating a CRM that needs to be able to store many facilities, customers, vendors, etc.
My question is how would I associate that profile with the company it belongs too? If I went to there profile page, for example, I should see what company they work for, regardless of what table the company is in.
I have 2 ideas but both seem flawed. One is to make a separate profile table for contacts for each. Example. vendor_profiles, customer_profiles, etc. This seems messy.
My other idea was to make a vendor_id, customer_id, etc column in the profile table, set them all to NULL by default, and if they belong to a vendor then my application code would check each for a number, and I think you get where I am going from there. Again, seems very messy, and inefficient.
I also considered grouping the Vendors, Customers, so on into one table and just setting a "type" but they all store very different info and are used in different, and often, relational ways.

Answer 1

Introduce a new organization table which unifies those aspects of vendor, customer,
facility and our_company that they all share in common:
CREATE TABLE organization (
organization_id serial4
type text);
CREATE TABLE profile (
profile_id serial4
user_id int4 REFERENCES user
organization_id int4 REFERENCES organization
...);
Then add an organization_id foreign key to vendor, customer, facility and our_company
so these tables can be joined to organization when the extra info in those tables are needed.
CREATE TABLE vendor (
vendor_id serial4
organization_id int4 REFERENCES organization
vendor_specific_field text
...);
Note that if you use "unique" names for id fields (such as organization_id instead of id) which have a consistent meaning across all tables, then you can JOIN ... USING syntax
SELECT *
FROM profile p
INNER JOIN organization o USING (organization_id)
INNER JOIN vendor v USING (organization_id)
WHERE o.type = 'vendor'
instead of
SELECT *
FROM profile p
INNER JOIN organization o ON p.organization_id = o.id
INNER JOIN vendor v ON v.organization_id = o.id
WHERE o.type = 'vendor'
which may improve readability and reduce potential errors in join conditions. (You'll never have to wonder what field in one table connects to the id field in another table.)