A vast amount of data is available in the physical world. Currently, the database management system necessitates a multitude of tables to contain this data. These tables may include numerous duplicate records, both in sorted and unsorted formats. Hence, the task of getting a specific or unique record from these tables becomes a daunting issue in the absence of limits or limitations.
Keys ensure that there are no duplicate records within rows or tuples. Let's explore the concept of keys in a database management system (DBMS).
In a database management system (DBMS), keys are attributes or groups of attributes that allow for the unique identification of a row or tuple within a relation or table. They create links between several tables and help to uniquely identify a row by using one or more columns in the table. Keys are essential for identifying certain records or rows in a table, and they function as a way to locate a singular and unique record or row in the database. This article will examine the significance of keys in a database management system (DBMS) and its primary classifications.
The Significance of Keys in Preserving Database Integrity
Keys are employed in a database to establish various forms of integrity constraints. On the other hand, a table is a collection of records that relate to various events in a certain relationship. These tables may contain several records, some of which may be duplicates.
Therefore, it is imperative to establish a unique and clear identification for each of these documents, ensuring the elimination of any duplication. This problem is efficiently solved by using keys. Keys in DBMS are crucial for guaranteeing the uniqueness and segregation of records, hence mitigating the related difficulties.
Types of Keys in DBMS
Primary Key
This type of keys in DBMS refers to a column that uniquely identifies all the records within that table. A table has one primary key only, and this key must not contain repeated or duplicated values across its rows. Each value within the primary key must be unique, with no repetitions allowed.
Applying the PK (PRIMARY KEY) constraint to a column or set of columns ensures that they cannot have null values or duplicates. Furthermore, any foreign key that references the primary key is unable to modify the values present in the primary key.
It guarantees that each entry in a table can be uniquely identified.
The primary key supports data integrity by prohibiting redundant or duplicate records by ensuring uniqueness.
Primary keys are often indexed by the DBMS, enhancing the speed of data retrieval operations.
The primary key has a critical role to play in building associations between tables.
Uniqueness is the most crucial element while selecting this key in DBMS. It means that this column’s value does not occur in any other table row.
In the following table, student id is the primary key.
Candidate Key
Candidate keys play a vital role in upholding the integrity and consistency of a database. The purpose of this key in DBMS is to guarantee each row’s uniqueness and independent identification within a table. Additionally, candidate keys enforce relationships between tables, ensuring data integrity and maintaining overall database consistency.
It must have distinct values.A candidate key in SQL can have a variety of qualities, but it must not include null values and must have at least the bare minimum of fields to guarantee uniqueness.
These keys in DBMS are essential for preserving a database’s consistency
and integrity. They are used to enforce connections between tables and
guarantee that each row in a database is distinct and can be recognized
independently.
In the following table, the primary keys are student id, roll number and email id.
Differences Between Primary and Candidate keys
A primary key is a column that allows each entry in a database to be identified only once. It is selected as the primary key for the table from the list of potential keys. A column that can uniquely identify each record in a database is sometimes referred to as a candidate key. It might be used as the primary key.
A primary key is a unique identifier for a record in a database table. A candidate key is also a unique identifier for a record in a database table.
There can be only one primary key in a table. There can be multiple candidate keys in a table.
The primary key enforces entity integrity, Candidate keys are potential candidates
The primary key is chosen by the database designer or administrator. A candidate key can be chosen from the set of candidate keys for a table.
Super Key
The collection of all keys enabling us to recognize every row in the table is a super key. This type of key in DBMS specifies that all the table columns that may identify the columns uniquely function as the super keys.
A super key must ensure that each record in a table is unique.
Nevertheless, the minimal collection of characteristics that can guarantee uniqueness should be a super key.
Multiple subsets that are likewise regarded as super keys can exist for a super key.
A super key’s only function is to identify specific table rows. Since a column with duplicates won’t be able to identify a unique row, you may often not tell which table it belongs to by picking any random column. Data retrieval is simplified, and this uncertainty is eliminated with this key in DBMS.
Foreign Key
To create connections between two accessible tables, we employ a foreign key. Every value in a column or collection must match the primary key in the referential table for the foreign key to function. We can preserve referential integrity and data integrity with the aid of a foreign key.
It is a key that serves as both a secondary key and a primary key in two different tables.
At any given time, it combines two or more relations.
They serve as cross-references for the tables.
Data in one table is connected to another through foreign keys. To develop a manner of cross-referencing two columns, a foreign key column in one table links to the column in another table with unique values.
Alternate Key
A key in DBMS might be selected as the main Key in a table in multiple ways. Any key that has the potential to replace the primary key but is not yet the primary key is considered an alternate key. It’s a prospective main key that hasn’t been selected yet.
Alternate keys refer to all keys that are not main keys.
It’s a backup key.
It has two or more fields that allow it to recognize two or more records.
These criteria are reiterated.
Since an alternate key is identical to a candidate key, its purpose and function are the same. This indicates that the columns in a table that may be used to identify each record in the database separately are additionally identified using an alternative key.
StudID, Roll No., and Email serves as the main keys. However, because StudID is the main key, Roll No. and Email is now the secondary key.
Compound Key
This key in DBMS contains two or more characteristics that recognise a specific record exclusively. It’s conceivable that none of the columns in the database are unique on their own. However, when paired with the additional column or columns, the composite key combination becomes unique. Each record in the table is to be uniquely identified using the database’s compound key.
Each record in a table must be guaranteed unique by a compound key.
The bare minimal collection of characteristics necessary to assure uniqueness should be a compound key.
A compound key attribute order is essential.
Compound keys are always constructed from two or more other tables’ primary keys. Both keys uniquely identify data in their respective tables, but both are required to do so in the table utilizing the compound key.
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