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what is the difference between primary key, unique key, surrogate key?
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Editorial / Best Answer
Kolta Sam- Member Since Jul-2011 | Jul 10th, 2011
Primary Key:
It is a visible key
It generated by user or application.
It could be changed by the user or application.
It could be queried
It used to form a relation between tables
It shouldn’t contain null value
It resemble table row
It is a unique identifier for a table object.
It contains only one key
It could contain numeric and strings characters.
It is an unique key which each row contain a distinct different key.
Example for it is a customer_Id.
It always starts by number one and second is two and so on but can starts with a different number.
Could created on one or more columns
No duplicate recordsSecondary Key:
It used to form a relation between tables.
It is alternate table key.
It used to search data with primary key
It could contains null value
It could contains more than one secondary key for each table
Created only on one columns
No duplicate records
It creates index clustered by default
Surrogate Key:It is invisible key for the user or the application.
It resembles database entity.
It generated by the system so it is invisible for user and application.
It shouldn’t contain null values
Only one surrogate key for each data entity
Its value is unique system wide.
Its value is never manipulated by the user or the application.
It never reused
It is frequently sequential number
It called synthetic key, an entity identifier, a system-generated key, a database sequence number, a factless key, a technical key, or an arbitrary unique identifier
No duplicate recordsgopi
- May 18th, 2018
Primary key not allow null values where as unique allows but both are alternates.
surrogate key serve as primery key in type 2 dimension tablesSukdya
- Nov 27th, 2017
Primary key doest not allow null values but unique key allows only one null value.
