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Difference between primary key and unique key with table

We explain unique key vs primary key or difference between primary key and unique key with table. A series of tables that have rows and columns that store information that is retrieved or used when required is called data. The data stored in the rows and columns is determined by the keys used in the table. A table has primary key, unique key, foreign key, etc. unique key vs primary key

A primary key constraint is used on a table to uniquely identify the rows in the table. In any data table, there is only one primary key. It does not take null values, nor does it allow duplicate keys.

A unique key in a table confirms that the data in each row and column is unique and does not repeat itself. In the table, there is more than one unique key. The unique key can have null values ​​and duplicate keys. A primary key is always unique, but the reverse is not always true. unique key vs primary key

What is the primary key?

One of the most important keys in a data table is the primary key. The primary key is a key that confirms the uniqueness of the data table. It uniquely determines the row of a table and therefore applies the entity integrity process. In a table, there is only one primary key, however the primary key value has two parts. The primary key can also be defined as the SQL constraint that uniquely identifies the rows in the record.

A primary key does not accept null values. The primary key also does not accept duplicate values. The default index on the primary key is clustered. The values ​​of the rows of a primary key in the table cannot be modified or deleted. A unique key can be associated with some other table as a foreign key.

The syntax for creating the primary key in the table is:

CREATE TABLE People (ID int NOT NULL, Lastname varchar (255) NOT NULL, Firstname varchar (255), Age int, PRIMARY KEY (ID));

What is the unique key?

Another key in the data table is the unique key. The unique key in the data table uniquely identifies rows other than the primary key. The function of the unique key is to apply conditions to the rows that make them unique. Its purpose is to ensure that the data in each row or column is unique and does not repeat itself. In a table, there is more than one unique key. Uniquely defines the data in the records. unique key vs primary key

A unique key can accept null values. It also takes duplicate values ​​in the table if and only if one or more of the key parts are null. The default index of the unique key is found. The values ​​of the rows and columns can be changed or modified. The unique key cannot be associated with any other table as a foreign key.

The syntax to create the unique key in the table is:

CREATE TABLE People (ID int UNIQUE. First name varchar (255) NOT NULL Last name varchar (255), Age int, UNIQUE KEY (ID));

Difference between primary key and unique key with table

The difference between primary key and unique key is that a primary key is used to uniquely identify a row of a table, the process of unique identification of rows is called entity integrity, a table only a unique key, while unique key places additional conditions to make the rows unique in addition to the primary key, a table can have more than one unique key.

Primary Key vs. Unique Key Comparison Table

Comparison parameter Primary key Unique key

Basic function The basic function of a primary key is to uniquely identify a row in a table. The basic function of a unique key is to apply additional conditions to a row to make it unique.
Number of keys on a table A table has only one primary key. A table can have more than one unique key.
Null value acceptance A primary key does not accept null values. A unique key can accept null values.
Indexing A primary key has a clustered default index. The default index on a unique key is not clustered.
Duplicate keys Duplicate keys are not allowed in a primary key of a table. Duplicate keys are allowed in a unique key in a table if one or more key parts are null.

Key differences

  • The basic function of a primary key is that it uniquely identifies rows in a table, whereas a unique key uniquely identifies distinct rows of the primary key. unique key vs primary key
  • The purpose of the primary key is to enforce the integrity of the entity, while the purpose of a unique key is to apply unique data.
  • The primary key is an SQL constraint to uniquely identify each record, while the unique key is an SQL constraint that does not allow the same value in the records.
  • In a table, there is only one primary key, whereas there can be more than one unique key.
  • A primary key in a table does not accept any null values, while a unique key accepts null values.
  • In a table, a primary key has a clustered default index, while a unique key has a non-clustered default index.
  • In the table, duplicate keys are not allowed in the primary key, while they are allowed in a unique key. unique key vs primary key
  • The values ​​of a primary key cannot be changed or deleted, while the values ​​of a unique key can be changed or deleted.
  • A primary key can be associated with other tables as a foreign key, while a unique key cannot be associated as a foreign key.
  • A primary key is always unique, while a unique key is not necessarily a primary key.

Final Thought

In a relational database, both the primary key and the unique key ensure column and table uniqueness. The primary key identifies unique records, on the other hand, the unique key prevents duplicate entries in the table. unique key vs primary key

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