Difference Between Primary Key And Foreign Key In Dbms
Key Differences Between Primary Key and Foreign Key in DBMS
Difference Between Primary Key And Foreign Key In Dbms
In a database management system (DBMS), a primary key is a unique identifier for each record in a table. It ensures the uniqueness and integrity of data by uniquely identifying each record and ensuring that no two records have the same primary key value. On the other hand, a foreign key is a field in a table that is related to the primary key of another table. It establishes a relationship between two tables by referencing the primary key in another table, ensuring data integrity and enforcing referential integrity constraints. In essence, the primary key uniquely identifies records within a table, while foreign keys establish relationships between tables.
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1 - Primary Key:
Primary key is a unique identifier for each record in a database table. It ensures each row in a table is distinct and cannot have duplicate values.
2) Foreign Key:
Foreign key establishes a relationship between two tables in a database. It is a field (or a set of fields) in one table that refers to the primary key in another table.
3) Uniqueness:
The primary key must be unique within a table, whereas foreign keys can have duplicate values in a table, but must have a corresponding unique value in the related table.
4) Purpose:
Primary key is used to uniquely identify records within a table, while foreign key is used to connect the records of one table to the records of another table.
5) Constraints:
Primary key constraint ensures that the values in the key column(s) of a table are unique and not null, while foreign key constraint ensures that values in the foreign key column(s) must exist in the referenced table's primary key column.
6) Indexing:
Primary keys are automatically indexed by databases for faster search and retrieval, while foreign keys can be indexed for optimization, but it is not mandatory.
7) Relationships:
Primary key defines the relationship within the table itself, identifying each record uniquely, while foreign key establishes relationships between tables, creating logical links between related data.
8) Data Integrity:
Primary key helps in maintaining data integrity by ensuring uniqueness and integrity of the records in a table, while foreign key helps in enforcing referential integrity between related tables.
9) Multiple Keys:
A table can have only one primary key, but can have multiple foreign keys referencing different tables, representing different relationships.
10) Cascade Actions:
Foreign keys often support cascade actions like on delete or update, where changes to the referenced key can propagate to related records for maintaining data consistency, whereas primary keys do not offer such cascade actions by default.
These points can serve as an informative overview for your training program on primary keys and foreign keys in database management systems.
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