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If you are engaged in database management, having a comprehensive grasp of how data is structured and accessed efficiently is crucial. One significant principle in databases involves the utilization of keys. These keys guarantee that records are identified uniquely and can be fetched promptly. Among the different varieties of keys, the one that frequently prompts inquiries is the Alternate Key.
In this article, we will guide you through all you need to comprehend regarding alternate keys in DBMS. So let’s dive in!
Table of Contents:
- What is a Key in DBMS?
- What is an Alternate Key?
- Characteristics of an Alternate Key
- How to Define Alternate Keys in SQL?
- Example of Alternate Key
- Importance of Alternate Key
- Difference Between Primary Key and Alternate Key
- Use Cases of Alternate Keys
- Conclusion
What is a Key in DBMS?
In an DBMS (Database Management System), a key is defined as a specific field or a combination of fields utilized to distinguish each record in a table uniquely. Keys are valuable for preserving data integrity and facilitating effective data retrieval. Without keys, locating and referencing specific records would be a sluggish process fraught with potential mistakes. Among the most frequently utilized keys, the Primary Key is essential for uniquely identifying each row. The Candidate Key functions as a field capable of serving as a unique identifier; the Alternate Key is a Candidate Key that has not been selected as the Primary Key; and the Foreign Key connects records across distinct tables. Together, these keys establish a robust framework for effectively organizing and managing relational data.
What is an Alternate Key?
An alternate key refers to any key within a database that uniquely identifies a row but is not selected as the primary key. When a table contains several candidate keys (all capable of uniquely identifying rows), only one key is designated as the primary key, while the others are regarded as alternate keys. These alternate keys serve as additional unique identifiers. They enable alternate methods to access data in the table, particularly when utilizing the primary key is unsuitable or impractical. The inclusion of alternate keys in a table grants flexibility and assures that multiple reliable methods exist for uniquely identifying records.
Characteristics of an Alternate Key
Below are some key characteristics of an Alternate Key:
- Uniqueness
Similar to a primary key, an alternate key must consist of unique values. This ensures that no two rows in the table have identical values for the alternate key. Maintaining this uniqueness is essential because it guarantees that the alternate key can accurately identify and differentiate each record correctly.
- Not-Null Constraint
An alternate key has the capacity to become a primary key. Thus, it must adhere to similar regulations, including that it cannot be null. Each record in the table must possess a value in the alternate column. This is critical because if any value is missing (null), that record cannot be identified uniquely, leading to concerns with data accuracy and integrity.
- Candidate Key
A candidate key is any field that can identify a row in a table uniquely. An alternate key is one of those candidate keys that has not been selected to be the primary key, yet possesses the attributes to qualify as one. If any issues arise with the current primary key regarding certain requisites, an alternate key could be utilized instead. The decision relies on the database design and what options are most suitable for that context.
How to Define Alternate Keys in SQL?
In SQL, an alternate key is not designated with a specific keyword. It is established by applying the UNIQUE constraint to a column or set of columns that contain unique values but is not the primary key. This ensures that no duplicate values can be inserted into that column, allowing it to function as a secondary unique identifier. Also, the term
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“alternate key” is not explicitly utilized in SQL; any column with the UNIQUE constraint, apart from the primary key, functions as the alternate key.
Below is an example for your reference.
Example:
-- Step 1: Create the table
CREATE TABLE Employees (
emp_id INT PRIMARY KEY,
email VARCHAR(100) UNIQUE,
phone VARCHAR(15) UNIQUE,
name VARCHAR(50)
);
-- Step 2: Insert sample data
INSERT INTO Employees (emp_id, email, phone, name) VALUES
(1, '[email protected]', '1234567890', 'emp1'),
(2, '[email protected]', '2345678901', 'emp2'),
(3, '[email protected]', '3456789012', 'emp3');
-- Step 3: Select from the table to generate output
SELECT * FROM Employees;
Output:
Explanation:
In the table above, emp_id serves as the primary key, while email and phone act as alternate keys. This is due to their uniqueness, allowing for the identification of each employee independently.
Example of Alternate Key
An alternate key essentially refers to a column (or a combination of columns) utilized for uniquely identifying a record in a table. They are not selected as the primary key and serve as a supplementary unique identifier. For instance, in an employee table, both email and employee_id may be unique, but if employee_id is designated as the primary key, email becomes the alternate key.
A further example is provided below for your reference.
Example:
-- Step 1: Create the table
CREATE TABLE Employees (
employee_id INT PRIMARY KEY,
email VARCHAR(100) UNIQUE,
name VARCHAR(50)
);
-- Step 2: Insert sample data
INSERT INTO Employees (employee_id, email, name) VALUES
(101, '[email protected]', 'emp1'),
(102, '[email protected]', 'emp2'),
(103, '[email protected]', 'emp3');
-- Step 3: Query the table to generate output
SELECT * FROM Employees;
Output:
Explanation:
In the query provided above, employee_id represents the primary key, while email is the alternate key. This distinction arises because it retains uniqueness but is not the primary identifier.
Importance of Alternate Key
Outlined below are key reasons highlighting the significance of alternate keys.
- Data Retrieval Flexibility
Alternate keys offer alternative methods for locating data within a table when the primary key is not accessible for a specific query. This flexibility ensures that various fields can be utilized to retrieve records, maintaining accuracy in results.
- Contribution to Normalization
In normalization processes within databases, alternate keys play a crucial role in reducing repetitive data and mitigating dependency issues. They enhance the structure and reliability of the database by providing additional pathways for data access and connection, thereby preventing errors or duplications.
- Adapting to Business Logic
In practical business situations, it is often necessary to identify records using methods other than the primary key. Alternate keys facilitate this need by offering alternative options, which enables unique data identification aligned with business requirements or data utilization.
Difference Between Primary Key and Alternate Key
The distinctions between the Primary Key and Alternate Key are summarized below in tabular form.
| Feature | Primary Key | Alternate Key |
| Definition | Considered the main key identifying rows uniquely. | A candidate key not selected as the primary key. |
| Uniqueness | A primary key must be unique. | An alternate key also needs to be unique. |
| NULL Values | Null values are not permitted in Primary Keys. | Null values are not allowed in Alternate Keys either. |
| Number per Table | Only one primary key is permitted per table. | Multiple alternate keys are allowed per table. |
| Used in Relationships | Frequently utilized as a Foreign Key in other tables. | Rarely applied in relationship cases. |
| Indexing | A primary key is automatically indexed. | Alternate keys may require manual indexing. |
| Selection | A primary key is selected from candidate keys. | The keys not chosen among candidate keys are termed alternate keys. |
| Example | Student_ID | Email, Phone Number |
| Constraints Applied | PRIMARY KEY | UNIQUE |
Use Cases of Alternate Keys
Highlighted below are some typical scenarios where alternate keys prove to be advantageous.
- User Authentication: Users may log in using their email or phone number. Both must be unique to ensure that the system accurately identifies the user.
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- Data Verification: Alternate identifiers assist in averting duplicate submissions in fields such as national ID or tax identification numbers.
- Query Enhancement: Alternate identifiers enable you to search or link tables utilizing distinct indexed fields other than the primary key.
Conclusion
A solid grasp of alternate identifiers will enable you to create more effective and dependable databases. An alternate identifier acts as a unique marker, similar to the primary identifier, but it is not selected as the principal identifier. It aids in bolstering data integrity, boosts the adaptability of querying, and enhances the database’s functionality.
By appropriately utilizing alternate identifiers, you can guarantee that your database is not only efficient but also robust against data duplication challenges. If you are constructing a relational database, always take into account the fields that could function as alternate identifiers, or you could encounter difficulties later on.
What is an Alternate Key in DBMS – FAQs
A table can indeed have one or more alternate identifiers. They could potentially be designated as primary identifiers, but they aren’t and continue to act as unique markers for each record.
Depending on the particular database in use, not every alternate identifier will create an index automatically. While some databases generate an index on columns defined with the UNIQUE constraint, others require manual indexing for optimal performance.
An alternate identifier can sometimes be a composite identifier as well. So long as the aggregation of the columns can distinctly identify each record, the appropriate columns will function as a composite primary identifier.
Yes, it is indeed feasible. If your current primary identifier is not suitable, a unique and non-null alternative can be designated as the primary identifier.
Alternate identifiers ensure that a column contains only one unique value with the UNIQUE constraint. Consequently, the quality of data is maintained by averting the entry of identical values more than once in those columns.
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