Differences Between Primary key and Secondary key 2024 Update

Keys are fundamental elements of the relational database. Today, we will look at the major differences between primary key and secondary key.

Differences Between Primary key and Secondary key 2024 Update

primary key is the first key to be understood as it uniquely identifies the particular record of any table. The primary key and foreign key, however, must not be confused with each other as they have a completely different definition as well as usage.

Both keys are the two most important and common types of keys used in relational databases.

Primary and Foreign Key

Keys have a more particular significance than establishing relationships. However, they also help with Referential Integrity and they are a major component of table-level integrity.

A primary key is a special key in a relational database that acts as a unique identifier for each record meaning it uniquely identifies each row/record in a table and its value should be unique for each row of the table. A foreign key, on the other hand, is a field in one table that links two tables together.

What’s Primary Key?

A primary key is a special key that uniquely identifies each record in a table. It is very important in the relational database to have a unique identifier in each row of a table.

And it is just the thing you need to uniquely identify a tuple within a table. A tuple represents a set of value attributes in a relational database.

A primary key may refer to a column or a set of columns in a relational database table used to implicitly identify all records in the table.

The primary key must be unique for each record as it acts as a unique identifier and it should not contain Null values. Each database must have one and only one primary key.

What’s Foreign Key?

foreign key refers to a field or a collection of fields in a database record that uniquely identifies a key field of another database record in some other table. In simple terms, it establishes a link between records in two different tables in a database.

It can be a column in a table that points to the primary key columns meaning a foreign key defined in a table refers to the primary key of some other table. References are crucial in relational databases to establish links between records which is essential for sorting databases.

Foreign keys play an important role in relational database normalization especially when tables need to access other tables.

Distinctions Between Primary Key and Foreign Key

1. Primary Key is a chosen candidate key that uniquely defines a tuple in a relation. whereas the other counterpart in a table refers to the primary key of other tables.

2. No two tuples in a relation carry duplicate values for a primary key attribute whereas foreign key accepts NULL value.

3. A primary key uniquely identifies a record in the relational database table.

4. A primary key is a combination of UNIQUE and Not Null constraints so no duplicate values can be allowed to have in a primary key field in a relational database table.

5. Before you delete a primary key value, make sure that value is not still present in the referencing foreign key column.

6. You can delete a value from the foreign key column without bothering, whether that value is present in the referenced primary key column of referenced relation.

7. Foreign key does not automatically create an index, clustered or non-clustered. You can manually create an index on the foreign key.



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