Secondary Key in DBMS
A Secondary Key in a Database Management System (DBMS) is a key used to search and retrieve records based on columns that are not the Primary Key. It is a way to index and access data quickly using other columns that may not be unique, but are important for querying.
How Does a Secondary Key Work?
Unlike the Primary Key, which uniquely identifies records, the Secondary Key is used to search and filter data in a table. It doesn’t necessarily have to be unique, and a table can have multiple secondary keys. It helps in faster retrieval of data when you’re looking for records based on certain column values, without using the primary key.
Example of a Secondary Key
Imagine a Customer table:
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Columns: CustomerID, Name, Email, Phone
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Primary Key: CustomerID
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Secondary Key: Email or Phone can be a secondary key. While these fields may not be unique (multiple customers can have the same email or phone number), they can still be used to search and retrieve customer data quickly.
Characteristics of a Secondary Key
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Non-unique: It may not be unique across records, unlike the primary key.
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Multiple Secondary Keys: A table can have multiple secondary keys.
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Search and Querying: It is used to perform searches, lookups, and queries efficiently based on non-primary key columns.
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Not Part of Primary Key: It is not the primary key and does not have to uniquely identify records.
When to Use a Secondary Key?
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When you need to search or filter data based on columns that are not the primary key.
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When you want to speed up queries by indexing other important columns like Email, Phone, or Address.
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When you want to create relationships based on columns that are not the primary key.
Advantages of a Secondary Key
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Faster Searches: Secondary keys help speed up searches and queries for non-primary key columns.
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Multiple Indexes: You can create indexes on different columns (secondary keys) for better data retrieval.
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Flexibility: Secondary keys provide flexibility in how you query data without relying on the primary key.
Disadvantages of a Secondary Key
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Data Duplication: Since secondary keys may not be unique, they can result in multiple entries for the same value.
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Extra Storage: Maintaining secondary keys requires extra storage space, as the database needs to store the additional index.
Conclusion
A Secondary Key is a useful tool in DBMS for improving data retrieval and query efficiency. While it doesn’t uniquely identify records like the primary key, it allows you to search and access data quickly based on other important columns