DIFFERENCESTerms And Technology

Difference between primary key and foreign key with table

We explain the difference between primary key and foreign key with table. The Database Management System (DBMS) is important in areas such as business, banking, airlines, telecommunications, and universities because it is an efficient and reliable method when it comes to creating, storing, and managing data in databases. The relational database management system (RDBMS) is the advanced form of DMBS structured especially for relational databases. These databases hold data in tables that contain rows and columns that symbolize an entry and an attribute respectively.

Keys are vital components of the relational database schema because they establish a link between two different tables and make sure to uniquely identify any row of data within a table. However, keys are of more specific importance than simply maintaining links. It helps to collect specific data from numerous rows that would have been intricate or even impossible at times if not for the keys. The two basic keys that help to establish and identify links between relational databases efficiently and are the primary keys and the foreign keys.

Without the primary key, a table cannot count as a relational database table. Because primary keys are used to uniquely identify a specific row of data, two or more rows cannot have similar primary keys. Rather, foreign keys are used to establish a relationship between the records in two different tables. However, unlike primary keys, we can have numerous foreign keys in a database.

the difference between the primary key and the foreign key is that the used primary key data contained within one or several columns in the table to identify each row uniquely while a foreign key is a column or several columns in a database that points to the primary key of a database record in some other table.

Comparison table between primary key and foreign key (in tabular form)

Comparison parameter Primary key Foreign key

Duplicate values Primary keys do not allow two rows to have the same values. Foreign keys allow the two rows to have the same values.
Insertion In primary keys, values ​​can be inserted even if the foreign key does not have that value. In foreign keys, you cannot insert values ​​if the values ​​are not present in the primary key.
Rank Each row in the relational database table can have only one primary key. A relational database table can have many foreign keys.
Clustered index Primary keys, by default, have a clustered index. Foreign keys do not have a clustered index.
Suppression When a value is to be removed, the value must be made not yet present in the foreign key reference table. When a value is to be removed, it can be done from foreign keys with ease.
Temporary tables Primary keys can be defined in a temporary table. Foreign keys cannot be defined in a temporary table.

What is the primary key?

A primary key refers to a particular choice of columns that uniquely determines the set of rows in a table. A primary key is a unique attribute that has a unique ID and is also considered a candidate key. There are two types of primary keys, that is, a simple primary key and a composite primary key. A simple primary key is a database table made up of a single column, while a composite primary key is a database table with more than one column.

The value of a primary key should never fluctuate or change because the primary key characterizes an importance in the database. So by changing the value it would result in a lot of confusion. The primary key must not contain a null value at the beginning so that no one can identify the value in that table. Also, no two rows have the same primary key, as this would not make the database unique. Therefore, there can only be one primary key for each row of data in a table.

The primary key is indexed by groups, which means that all the rows in the table are ordered. The primary key is primarily defined in a temporary table. When one is deleting rows from a table, one must be careful that the deleted value is not present in the foreign key column.

What is the foreign key?

A foreign key refers to a column in a database table that provides a link between two tables. When table 1 has a primary key of table 2, this attribute is the foreign key. Table 1 that has the foreign key is called the reference key, and the primary key in table 2 is called the reference relationship.

Unlike primary keys, foreign keys can contain null values, as they do not help identify a difference in the relationship because primary keys have already done this part of the work. Foreign keys can also accept duplicate values ​​unlike primary key and can have many or multiple foreign keys in a database, since foreign keys can have different attributes. However, foreign keys cannot have a clustered index.

Foreign keys cannot be defined in a temporary table. When adding a value in the foreign key column, one should make sure that the value is present in the primary key and that there are no restrictions when removing values ​​from a foreign key. External tables help maintain the integrity of the tables in the database. The database management system can prevent accidental deletion of any value.

Main differences between primary key and foreign key

  • Primary keys do not allow two rows in a database table to have duplicate values. Foreign keys allow two rows in a database table to have duplicate values.
  • In the primary keys attribute, values ​​can be inserted into the table even if the foreign key does not have that value in its column. In the foreign keys attribute, the values ​​cannot be inserted into the table if the values ​​are not present in the primary key database.
  • A primary key attribute can only have one primary key range in its table. A foreign key attribute can have a wide range of foreign keys in its table.
  • Primary keys have a clustered index, which means that all rows in the database relationship are ordered. Foreign keys do not have an automatic clustered index, but it can be done manually.
  • In primary keys, a value can be removed from the reference table by ensuring that the value is not present in the foreign key reference table. In foreign keys, the values ​​can be removed without any glitch, as it doesn’t matter whether the value is still present in the primary key reference table or not.
  • Primary keys can be determined in a temporary table. Foreign keys cannot be determined or applied to a temporary table.

Final Thought

In the database management system, keys play an important role in establishing relationships within a table and also between different tables. But to do so, we must ensure that the areas we use to maintain relationships between different tables must have comparable values ​​and the table must be made up of unique rows.

This article talks about the two most essential and common keys that create links between tables and help relational database management systems work efficiently. Primary keys and foreign keys are described in detail and are differentiated to help people clearly understand how different the two are, because although these terms may be similar in design, they perform different functions.

A primary key uses the data within a column or multiple columns to uniquely identify all the rows in a relational database table to avoid inserting a duplicate row of data, while a foreign key is used to link between two tables in a database.

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