Define primary key and give one example
Answers
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A candidate key chosen by the database designer to act as key is the primary key. An entity type may have more
than one candidate keys, in that case the database designer has to designate one of them as primary key, since there
is always only a single primary key in an entity type. The primary key can also be defined as the successful
candidate key
For example:
Roll_No can be used as a primary key of the entity as it would always be unique
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ANSWER
A primary key is a special relational database table column (or combination of columns) designated to uniquely identify all table records.
A primary key’s main features are:
It must contain a unique value for each row of data.
It cannot contain null values.
A primary key is either an existing table column or a column that is specifically generated by the database according to a defined sequence.
For example, students are routinely assigned unique identification (ID) numbers, and all adults receive government-assigned and uniquely-identifiable Social Security numbers.