Can a primary key be a foreign key in multiple tables?
Yes, it is possible.
You will need to define 2 FKs for 3rd table.
Each FK pointing to the required field(s) of one table (ie 1 FK per foreign table)..
Can a column be a primary and foreign key?
The structure and data type of PRIMARY KEY and FOREIGN KEY must be same. … The values of the FOREIGN KEY columns in each row of the referencing table have to match with the values of the corresponding primary key columns of a row in the referenced table.
What is the difference between a primary key and a foreign key?
Primary key uniquely identify a record in the table. Foreign key is a field in the table that is primary key in another table. By default, Primary key is clustered index and data in the database table is physically organized in the sequence of clustered index. …
Can a table have no primary key?
Every table can have (but does not have to have) a primary key. The column or columns defined as the primary key ensure uniqueness in the table; no two rows can have the same key. The primary key of one table may also help to identify records in other tables, and be part of the second table’s primary key.
Can foreign key be duplicate?
By default there are no constraints on the foreign key, foreign key can be null and duplicate. while creating a table / altering the table, if you add any constrain of uniqueness or not null then only it will not allow the null/ duplicate values.
Can a foreign key be part of a primary key?
This is not possible. The foreign key can not refer to part of composite primary key of other table. Because it is supposed to be one-to-one relationship and if you refer just part of primary-key, there might be more than one parent record available, which is neither allowed nor possible.