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Foreign Key A foreign key is generally a primary key from one table that appears as a field in another where the first table has a relationship to the second. In other words, if we had a table A with a primary key X that linked to a table B where X was a field in B, then X would be a foreign key in B.
Describe the major types of keys including primary, candidate, and foreign. Describe how one-to-one, one-to-many, and many-to-many binary relation-ships are implemented in a relational database. Describe how relational data retrieval is accomplished in concept with the select, project, and join operators.
A Key is an attribute or a set of attributes in a relation that identifies a tuple (record) in a relation. The keys are defined in a table to access or sequence the stored data quickly and smoothly. They are also used to create relationship between different tables.
A foreign key is a column (or group of columns) used in a relational database to link data between tables. This tutorial will introduce you to foreign keys and show you how to use them in SQL.
Foreign key constraint: Value in one relation must appear in another.
• Foreign key: Identifies the relationship between different entities. When a copy of the primary key for one entity is included in the collection of attributes of another entity, the copy of the primary key held in the second entity is known as a foreign key. Identifier (super key) design criteria • Should not change in value
Foreign key: Set of fields in one relation that is used to `refer’ to a tuple in another relation. Must correspond to primary key of the second relation. Like a `logical pointer’. E.g., sid in Enrolled is a foreign key referring to Students: Enrolled(sid int, cid char(20), grade char(2))
