Upuść klucz obcy
ALTER TABLE table_name
DROP CONSTRAINT fk_name;
SmokeFrog
ALTER TABLE table_name
DROP CONSTRAINT fk_name;/*Creating Foreign Key Constraint*/
ALTER TABLE ForeignKeyTable ADD CONSTRAINT ForeignKeyTable_foreignKeyColumn_FK
FOREIGN KEY (foreignKeyColumn) REFERENCES PrimaryKeyTable (PrimaryKeyColumn)create table Jobs(
job_id number not null,
job_title varchar(30),
min_salary number,
max_salary number
);
create table job_history(
employee_id number not null,
start_date date,
end_date date,
job_id number not null,
department_id number
);
alter table jobs add constraint pk_jobs primary key(job_id);
alter table job_history add constraint fk_job foreign key(job_id) references jobs(job_id);CREATE TABLE Orders (
order_id INT PRIMARY KEY,
customer_id int REFERENCES Customers(id)
);FOREIGN KEY (fk_col_name)
REFERENCES target_table_name (pk_col_name);
A foreign key is an attribute of a relation (subordinate/dependent)
that points to the primary key of another relation (main/master)
FK is used to create a many-to-one (one-to-many) relationship.