Can primary key and foreign key have same name?
To facilitate keeping key variable names consistent, and to provide for programs that do natural joins, foreign keys have the same name as is used in the table in which they are the primary key.
Can a foreign key be a primary key?
Yes, it is legal to have a primary key being a foreign key. This is a rare construct, but it applies for: a 1:1 relation. The two tables cannot be merged in one because of different permissions and privileges only apply at table level (as of 2017, such a database would be odd).
How foreign keys represent the relationships?
The matching of foreign key values to primary key values represents data relationships in a relational database. The customer number column in the order table is a foreign key that matches the primary key of the customer table. It represents the one-to-many relationship between customers and the orders they place.
What is purpose of foreign key?
A foreign key is a column or group of columns in a relational database table that provides a link between data in two tables. It acts as a cross-reference between tables because it references the primary key of another table, thereby establishing a link between them.
Can foreign key be part of composite primary key?
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.
Does a foreign key have to be unique?
Any primary key must be unique and non-null. Therefore if the child table has a foreign key referencing the parent’s primary key, it must match a non-null, unique value, and therefore references exactly one row in the parent table. In this case you can’t make a child row that references multiple parent rows.
What data problem does a foreign key solve?
Foreign keys help maintain the integrity of your data, but they can make it a challenge to load all data, handle cyclical references, and keep changes in sync. Now you know what some of the issues are and what approaches are available for solving them.
What is a foreign key example?
A foreign key is a set of attributes in a table that refers to the primary key of another table. For example, a table called TEAM may have an attribute, MEMBER_NAME, which is a foreign key referencing a candidate key, PERSON_NAME, in the PERSON table.