SQL创建表相同的主键和外键

Question

Can i know if i can use a create statement to declare an attribute both primary & foreign key?

Like:

CREATE TABLE personal_partner (
    partner_id NOT NULL PRIMARY KEY FOREIGN KEY REFERENCES partner(partner_id)
)

Also, do i have to add a unique constraint on a primary key?

Thanks

Answer 1

Yes we can.

create table partner ( partner_id INTEGER NOT NULL PRIMARY KEY)

create table personal_partner ( partner_id INTEGER NOT NULL PRIMARY KEY FOREIGN KEY REFERENCES partner(partner_id))

Answer 2

-- You can create both PK and FK on personal_partner (partner_id)
-- There should be a PK or Unique constraint on the referenced table\\column (partner(partner_id)).
-- The Primary Key (PK) consists of an Unique Constraint + NOT NULL constraint therefore you shouldn't "worry" about the need to add other unique constraint in table personal_partner, that is automatically created when defining column(s) as PK.
-- The below code works and should be what you need:

CREATE TABLE partner(
partner_id INT PRIMARY KEY -- or unique constraint, if this may contain NULLs
)

CREATE TABLE personal_partner (
partner_id INT NOT NULL PRIMARY KEY,
CONSTRAINT FKtoPartner FOREIGN KEY (partner_id) REFERENCES partner(partner_id)
)