Different Types of Keys in RDBMS

Keys are essential in relational database management systems (RDBMS) as they establish linkages between tables and ensure data integrity. Different varieties of keys are employed to distinctly identify records in a table and make connections between tables. The following are the various types of keys in a Relational Database Management System (RDBMS):

1. The primary key (PK)

A primary key is a singular column or a group of columns that unequivocally identifies every individual record within a database. The data must consist of distinct values and cannot include any NULL values. Each table is limited to having a single primary key. The primary key is utilized to build connections across tables and enforce the integrity of entities.

2. Foreign Key (FK)

A foreign key is a column or a set of columns in a database table that refers to the primary key of another table. It establishes a relationship between the two tables, allowing data to be linked and ensuring data integrity. A foreign key is a column or a group of columns in a table that references the primary key of another table. It makes a connection between two tables by referencing the primary key of one table as a foreign key in another. Foreign keys are used to maintain referential integrity, which guarantees the consistency of relationships between tables.

3. Unique Key

A unique key functions similarly to a primary key by guaranteeing the uniqueness of values within a column or a group of columns. A unique key differs from the primary key in that it permits the inclusion of NULL values. A table can include numerous unique keys, but it can only have one primary key.

4. Composite Key 

A composite key is a combination of two or more keys that uniquely identifies a record in a database. A composite key is a key composed of many columns that serves to uniquely identify records. It is employed when a solitary column cannot provide uniqueness, but the amalgamation of numerous columns can. Composite keys are commonly employed in junction tables to represent many-to-many relationships.

5. Super Key

A super key is a collection of one or more columns that, when combined, uniquely identify each individual record within a database. It may contain an excessive number of columns that are not essential for creating a minimal unique identity. A super key is an encompassing concept that encompasses primary keys, unique keys, and other candidate keys.

6. Candidate Key

A candidate key is a collection of one or more columns that can unequivocally identify every record in a table. It fulfills the requirements of uniqueness and irreducibility (minimum number of columns). Among the candidate keys, a specific one is chosen to serve as the primary key.

7. Alternate Key 

An alternate key refers to a candidate key that is not selected as the primary key. Although the primary key serves the aim of uniquely identifying data, additional keys can also be utilized to achieve uniqueness and facilitate searches.

8. Natural Key

 A natural key is a key that is obtained from the inherent attributes of the data, such as a Social Security Number, email address, or product code. Natural keys are commonly employed when the data inherently possesses a distinct identity.

9. Surrogate Key

A surrogate key is a unique identifier that is assigned to a record in a database table. It is often generated by the system. A surrogate key is a key generated by the system and utilized as the primary key. It does not originate from the data but functions as a replacement for a natural key. Surrogate keys are beneficial in cases when native keys are intricate, prone to modification, or unavailable.

Comprehending and effectively applying these keys is crucial for creating a well-organized and standardized relational database schema. The selection of keys is contingent upon the precise demands of the application and the interconnections among tables.

Happy Exploring!