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In the tangible realm, an extensive quantity of data is accessible. Presently, the DBMS requires numerous tables to accommodate this data. These tables may contain many duplicate records, both sorted and unsorted. Consequently, retrieving a distinct or particular record from these tables without constraints or limitations poses a formidable challenge.
A novel concept called "Keys" has emerged to address these challenges. Keys serve the purpose of guaranteeing the absence of duplicate records within rows or tuples. Let's delve into understanding of keys in DBMS.
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In a DBMS, KEYS are attributes or sets of attributes that enable the identification of a row or tuple within a relation or table. They establish connections between different tables and assist in uniquely identifying a row by utilizing one or more columns in the table. Keys play a vital role in locating distinct records or rows within a table, and they serve as a means to find a unique record or row within the database. In this article let’s explore the importance of keys in DBMS and its major types.
Keys are utilized in a database to establish different types of integrity constraints. Conversely, a table is a compilation of records pertaining to diverse events within a given relation. Many records may exist within these tables, some of which could be duplicates.
Hence, it becomes necessary to uniquely and distinctly identify each of these records, eliminating any duplications. This predicament is effectively resolved through the implementation of keys. Keys in DBMS play a pivotal role in ensuring the uniqueness and separation of records, alleviating the associated challenges.
Now we have understood what is a key in DBMS, let’s look at the major types of keys in DBMS in detail.
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.
For the following reasons, the primary key is crucial in a database management system (DBMS):
In this example, the student ID is the primary key.
StudID |
Roll No | First Name | Last Name | |
1 |
11 | Tom | Prince | abc@gmail.com |
2 | 12 | Nick | Wright | |
3 | 13 | Dana | Natan |
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.
StudID |
Roll No | First Name | Last Name | |
1 | 11 | Tom | Prince | |
2 |
12 | Nick | Wright | xyz@gmail.com |
3 | 13 | Dana | Natan |
The candidate keys Roll No., Stud ID, and Email in the table enable us to identify each student record uniquely.
Primary Key | Candidate Key |
---|---|
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. |
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.
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'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.
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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.
Dept code |
Dept name |
121 |
Science |
213 |
English |
513 |
Computer |
Teacher ID |
Fname | Lname |
B002 |
David |
Warner |
B017 | Sara |
Joseph |
B009 |
Mike |
Brunton |
In this Key in DBMS example, we have two tables: instructor and department at a school. However, it is hard to distinguish which instructor is assigned to which division.
We can link the two tables in this table by adding the Foreign Key in Deptcode to the Teacher name.
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.
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.
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StudID |
Roll No | First Name | Last Name | |
1 | 11 | Tom | Prince | |
2 |
12 | Nick | Wright | xyz@gmail.com |
3 | 13 | Dana | Natan |
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.
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.
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.
Order No |
Product ID | Productname | Quantity |
B005 |
JAP1024 | Mouse |
5 |
B005 | JHD1345 | USB |
10 |
B005 |
KDL0973 | LCD Monitor | 20 |
B002 | FRG1204 | USB |
6 |
B004 |
JUW1287 | Laser printer |
2 |
Below is the example of this key in DBMS:
OrderNo and ProductID cannot be the main key since they do not uniquely identify a record. A compound key combining the Order ID and Product ID might be utilized to identify each record uniquely.
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.
Here's a comparison between different types of keys in a relational database management system (DBMS) presented in a table format:
Key Type | Definition | Uniqueness | Null Values | Purpose | Index | Usage | Alteration |
---|---|---|---|---|---|---|---|
Primary Key | Uniquely identifies each record in a table. | Required | Not Allowed | Data integrity, record identification. | Creates Unique Index | Within same table | May be complex, impact other tables. |
Foreign Key | Establishes a relationship between tables. | Not Required | Allowed | Data consistency, relationship maintenance. | May create Index | Between tables | More flexible for maintenance. |
Candidate Key | Alternative unique keys that could be primary keys. | Required | Not Allowed | Backup primary key options. | May create Index | Within same table | May become primary key. |
Super Key | Combination of attributes that uniquely identify. | Required | Allowed | Conceptual, not enforced. | May create Index | Conceptual use | N/A |
Composite Key | Combined attributes used as a single key. | Required | Not Allowed | Specialized unique identification. | Creates Composite Index | Within same table | May be complex, impact performance. |
Unique Key | Ensures column(s) have unique values. | Required | Allowed | Enforce uniqueness, no primary key. | Creates Unique Index | Within same table | May be used as primary key. |
Surrogate Key | Artificial keys assigned for record identification. | Required | Not Allowed | Enhanced data privacy, data warehousing. | Creates Unique Index | Within same table | Generally static, non-changing. |
In this guide we have covered all about the keys in DBMS, their major types with example. When developing a database, keys and functional dependencies are crucial components. The distinction between excellent and poor database design may also be made using these ideas. Normalization is the final step in eliminating redundancies and improving database performance, which uses all the concepts discussed in this article. Also check out this Business Analytics course by Hero Vired to get master in niche.
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