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Stack Overflow for Teams A private, grid k520 bitcoin home for your team’s questions and answers. M9 1a8 8 0 1 0 0 16A8 8 0 0 0 9 1zm. I have a confusion between primary key and unique key. Please help me where should I create primary and unique key.

I mean in which situation we create unique key or primary key . In some DBMS it cannot be NULL – e. Also want to add on that primary key can be created on multiple columns, e. This is called composite primary key. Unique key can be null and may not be unique Means ? PratikCJoshi He probably means that the can be multiple rows with null on the otherwise unique key. It’s a column or a group of columns that can identify a uniqueness in a row.

It’s also a column or group of columns that can identify a uniqueness in a row. PK creates a Clustered index and UK creates a Non Clustered Index. 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. Typically, business needs to record and process information of those business entities. These business entities are identified within a whole business domain by a Key. For a DB-Table, there are so many keys are exist and might be eligible for Primary Key.