what is difference primary key and uniqkey?

Shah Sahil

8y1.4kLearn iOS Programming

6 Replies

Know the answer? Post it — somebody with the same question will find it here.

Mageshwaran R6y ago
Hi
Primary key will not accept NULL values whereas Unique key can accept one NULL value.
A table can have only primary key whereas there can be multiple unique key on a table.
A Clustered index automatically created when a primary key is defined whereas Unique key generates the non-clustered index
Nitin Sontakke8y ago
@Packia, Brajesh Kumar's post does mention that in the table.
Packiaraj Santhiyagu8y ago
Hi,

Please google it you will get lot of answers.

Both are enforce unique value.

Only one differnt is other guys forget say here.

Primary key do not accept null value
Unique key accept only one null value.
Nitin Sontakke8y ago
The best approach, for the questions like this, is to paste your question in google search and hit enter.

You will get loads and loads of answers.
Brajesh Kumar8y ago
Primary Key:
There can only be one primary key in a table
In some DBMS it cannot be NULL - e.g. MySQL adds NOT NULL
Primary Key is a unique key identifier of the record
Unique Key:
Can be more than one unique key in one table
Unique key can have NULL values
It can be a candidate key
Unique key can be NULL and may not be unique
Unique Key (UK): It's a column or a group of columns that can identify a uniqueness in a row.

Primary Key (PK): It's also a column or group of columns that can identify a uniqueness in a row.

So the Primary key is just another name for unique key, but the default implementation in SQL Server is different for Primary and Unique Key.

By Default:
PK creates a Clustered index and UK creates a Non Clustered Index.
PK is not null, but UK allows nulls (Note: By Default)
There can only be one and only one PK on a table, but there can be multiple UK's
You can override the default implementation depending upon your need.
It really depends what is your aim when deciding whether to create a UK or PK. It follows an analogy like "If there is a team of three people, so all of them are peers, but there will be one of them who will be a pair of peers: PK and UK has similar relation.". I would suggest reading this article: The example given by the author may not seem suitable, but try to get an overall idea.
Amit Kumar8y ago
Hi,
Use below and read it.

https://www.c-sharpcorner.com/blogs/difference-between-primary-key-unique-key-and-foreign-key1