what is primary key,unique key, foreign key? can u teach me
in simple language?
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Answer Posted / charu gautam
primary key:- the primary key of a relational table uniquely
identifies each record in the table. it can either be a
normal attribute that is guaranteed to be unique . such as
social security number in a table with no more than record
per person or it can be generated by the D B M S .such as a
globally unique identifier ,or G U I D, in microsoft SQL
server primary key may consist of a single attribute or
multiple attribute in combination.
foreign key:- A foreign key is a field (or fields) that
points to the primary key of another table.The purpose of
the foreign key is to ensure referential integrity of the
data.In other words ,only values that are supposed to appear
in the database are permitted.
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