What Is A Unique Key in DBMS?

What Is A Unique Key?

A unique key in a database management system (DBMS) is a condition that is assigned to a certain number of dataset columns to guarantee that the information stored in those columns is distinct for every row in the table. This indicates that in the designated columns, no two records may have an identical combination of values. The reliability of the data is monitored by the unique key restriction, which prohibits copy or null entries in the designated columns.

In database management systems, a unique key serves as a means of uniquely identifying a tuple within a table and averting value duplication.

Role Of Unique Key

A unique key in DBMS serves many critical functions in a database management system (DBMS):

1. Maintains data reliability- Unique keys ensure that data stored in a database is accurate and consistent by prohibiting entry replication. By doing this, the possibility of contradicting information is removed, and accurate data display is guaranteed.
2. Determines distinct entities- Order numbers, merchandise codes, and customer IDs are examples of distinct keys that serve as designations for specific entities in a table. This facilitates the retrieval, modification, and analysis of individual data points.
3. Allows table associations to exist- Unique keys provide the basis for creating associations between records. In order to facilitate data connection and table movement, foreign key restrictions make connections to unique keys within various tables.
4. Enhances the speed of queries- Table index creation is possible with unique keys. By offering a rapid and effective means of locating certain data depending on the distinct key columns, these types of indexes expedite the handling of queries.
5. Avoids data duplication- Reducing redundant entries using distinct keys minimizes the replication of information and maximizes storage capacity. In addition to reducing needless data upkeep, this increases database reliability.
6. Ensures the validity of data- During the addition and modification of data, unique key restrictions serve as an inspection tool. By preventing the introduction of identical values, they preserve the established data constraints and guarantee data security.
7. Helps with data analysis- By offering a trustworthy point of departure for organizing, arranging, and classifying data, unique keys facilitate the efficient evaluation of data. This enables in-depth examination and accurate recommendations.

Importance Of Unique Key

1. Data Accuracy- Every entry in a table stored in a database is guaranteed to be uniquely identifiable by its unique key. This keeps the data from becoming redundant or inconsistent, preserving the data's quality. Record duplication may cause mistakes, disorientation, and challenges in data analysis.
2. Recognition of Documents- A dependable and distinct identifier for every entry in a database is provided by unique keys, particularly when they are employed as the main keys. Establishing connections in the context of a relational database is necessary for identifying and connecting entries across several tables.
3. Table Interrelationships- In a database with relationships, unique keys are frequently used as the foundation for defining associations amongst tables. An association between associated information can be established when a foreign key within one table references a unique key in another. Maintaining constant connections is made easier, and the confidentiality of references is guaranteed.
4. Query Enhancement- For the designated columns, unique entries are usually created using unique keys. Through the quick location of individual entries in a table, clustering facilitates simpler retrieval of data procedures, such as SELECT queries. For databases that include enormous datasets, this optimization is essential.

How Is A Unique Key Different From A Primary Key?

Relational databases employ two different kinds of constraints—unique key and primary key—to guarantee that entries in the column or set of columns are different.

1. Uniqueness:

• Unique Key: When a unique key condition is applied, all rows within the table are guaranteed to have distinctive data in the designated column or columns. A table may contain numerous distinct keys.
• Primary key: A primary key is a particular kind of identifiable key that has the additional requirement that its value items must not be null in addition to enforcing individuality. A single main key is also permitted for each table.

2. Values With No Data:

• Unique Key- Permits null values to exist in the columns designated as unique keys.
• Primary Key- Keeps null values out of the columns that contain the primary key.

3. Number Of Keys:

• Unique Key- Several distinct keys that enforce authenticity on various columns can be included in a table.
• Primary Key- A primary key is a special key that distinctly distinguishes each entry in a table, and it can only have a single primary key.

4. Indexing:

• Unique Key- For the purpose of improving query efficiency, the database system could instantly build an index for a distinct key.
• Primary key- To enhance retrieving information, a main key is automatically indexed.

Unique Key Example

Example 1: Customer table

Columns: customer_id (primary key), email, phone_number

Unique key: email, phone_number

Rationale: This ensures that each customer has a unique email address and phone number, preventing duplicate entries and improving data quality.

Example 2: Product 

Columns: product_id (primary key), product_code, product_name

Unique key: product_code

Rationale: This guarantees that each product has a unique identifier (product code) and eliminates the possibility of duplicate product entries.

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Conclusion

Ultimately, unique keys are essential to maintaining effectiveness and data consistency in a database management system. They protect against repeated entries by displaying accurate information and avoiding discrepancies. They also act as unique entity IDs, making it possible to retrieve and analyze data effectively. Their function in building linkages between tables and optimizing query speed underscores their significance in database architecture.

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FAQs

1. Can a table have multiple Unique Keys?

Yes, numerous Unique Keys may be specified on various columns or a mix of columns in a table. The defined columns are subject to separate uniqueness enforcement by each Unique Key.

2. Can a Unique Key contain null values?

It is possible for a Unique Key to have a single null value. This indicates that for whatever column or columns are specified as the Unique Key, one entry in the database may have a null value.

3. How is a Unique Key different from a Candidate Key?

Any grouping of columns that distinguishes each row in a database is called a candidate key. A maximum of one Candidate Key may be selected to be the Primary Key in a table. You can classify all other candidate keys as unique keys.

The fundamental distinction is seen in the constraints:

• With the exception of one null value, the unique key ensures uniqueness.
• No null values are permitted, and the candidate key strictly enforces uniqueness for every row.

4. Can I change the Unique Key of a table after data has been inserted?

Yes, after data has been added, the Unique Key of a table may be changed.