Information about Compound Key
In database design, a compound key (also called a composite key or concatenated key) is a key that consists of 2 or more attributes.
No restriction is applied to the attributes regarding their (initial) ownership within the data model. This means that any one, none, or all, of the multiple attributes within the compound key can be foreign keys. Indeed, a foreign key may itself be a compound key.
Compound keys almost always originate from attributive or associative entities (tables) within the model, but this is not an absolute.
No restriction is applied to the attributes regarding their (initial) ownership within the data model. This means that any one, none, or all, of the multiple attributes within the compound key can be foreign keys. Indeed, a foreign key may itself be a compound key.
Compound keys almost always originate from attributive or associative entities (tables) within the model, but this is not an absolute.
See also
External links
- Composite Inverse Functional Properties: for an equivalent notion in the Semantic Web
In computer science, data modeling is the process of creating a data model by applying a data model theory to create a data model instance. A data model theory is a formal data model description. See database model for a list of current data model theories.
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In computer science, data modeling is the process of creating a data model by applying a data model theory to create a data model instance. A data model theory is a formal data model description. See database model for a list of current data model theories.
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In the context of relational databases, a foreign key is a referential constraint between two tables.[1] The foreign key identifies a column or a set of columns in one (referencing) table that refers to a column or set of columns in another (referenced) table.
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A relational database is a database that conforms to the relational model, and refers to a database's data and schema (the database's structure of how that data is arranged).
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In the relational model, a candidate key of a relvar (relation variable) is a set of attributes of that relvar such that
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- (1) at all times it holds in the relation assigned to that variable that there are no two distinct tuples with the same values for these attributes and
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In relational database design, a unique key or primary key is a candidate key to uniquely identify each row in a table. A unique key or primary key comprises a single column or set of columns.
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An alternate key (or secondary key) is any candidate key which is not selected to be the primary key (PK).
For example, a relational database with a table "employee" could have attributes like "employee_id", "bank_acct_no", and so on.
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For example, a relational database with a table "employee" could have attributes like "employee_id", "bank_acct_no", and so on.
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In the context of relational databases, a foreign key is a referential constraint between two tables.[1] The foreign key identifies a column or a set of columns in one (referencing) table that refers to a column or set of columns in another (referenced) table.
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In relational database design, a unique key or primary key is a candidate key to uniquely identify each row in a table. A unique key or primary key comprises a single column or set of columns.
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