If the key is part of a linking table it can be.
The foreign key is used as a reference in a table to the primary key of another table. For example: consider a table employee with id(primary key), name, address,department_id(foreign key) as its fields.Another table department with fields department_id(primary key) and dept_name. So, department_id is primary key in department table and foreign key in employee table.
In some database systems, A Foreign Key that is set on one column (the child column ) has to point to another column (the parent column ) that is indexed. The parent column could be a primary key, since a primary key creates an index. Primary keys also keep values in the parent column unique, which can ensure unique records in the parent column's table; having a unique key on the child column can further enforce unique data that links with the unique records in the parent column .
foreign key in the sql is to query on the related information aavailable in the table.
A primary key is always unique and not null. It is prefer to choose a field that is unique like roll number . But to choose Last name as a primary key is not a good option as two people can have same last name.A Last name field is not a good one for a primary key. A primary key cannot have duplicate values. A last name field is highly likely to have duplicate values, so it should not be used as a primary key.
condition key is a simply one of the open source
The foreign key is used as a reference in a table to the primary key of another table. For example: consider a table employee with id(primary key), name, address,department_id(foreign key) as its fields.Another table department with fields department_id(primary key) and dept_name. So, department_id is primary key in department table and foreign key in employee table.
Because the foreign key is copied from the primary key of the parent table
Foreign keys are used to link one database with another. A primary key is an attribute of a record that allows users to identify information.
A primary key is one that uniquely identifies a record . Also there are cases when primary key of one file appears in another file. In that case the key is called Foreign key.
In sql you use primary key more than one column in a table
It is not mandatory that is must be a primary key but it must be a unique key in the other table.
We designate one of the candidate key of a relation to be a primary key because that primary key is use for any foreign key references.
3 Foreign key
It is the DBMS that ensures the value of the foreign key matches another table's primary key when referential integrity constraints are enabled within the DBMS
A primary key is an attribute (or combination of attributes) that uniquely identifies each row in a relation. A primary key is designated by underlining the attribute name. The primary key of an entity set allows us to distinguish among the various entities of the set. A foreign key is an attribute in a relation of database that serves as the primary key of another relation in the same database.
foreign key constraint defines a column or combinations of columns whose values match the primary key of another table.
False. A foreign key is a primary of one table that is in another table. A foreign key can be repeated, so it does not uniquely identify records in the table where it is a foreign key.