Primary Key in DBMS
Primary Key in DBMS
The primary key of a relational table uniquely identifies each record of the table.
There are two types of primary key.
- simple primary key
- composite primary key
1.Simple primary key:-
Simple primary key consists of only one field.
2. composite primary key
A composite primary key is made up of more than one field.
Defining the primary key: –
- Primary key is unique.
- There can be only one primary key in any table.
- It can be single or multi column, we call multi column primary key as composite primary key.
- Composite primary key can have maximum 16 columns.
- It does not contain null values.
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