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what is primary key,unique key, foreign key? can u teach me
in simple language?
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Answer Posted / sathish
1)Primary key is unique key but foriegn key always refers
to
primary key.
2) Primary keys enforce entity integrity by uniquely
identifying entity instances. Foreign keys enforce.
3)Primary key is unique
primary key is not NULL and
foreign key is NULL
foreign key reference as Primary key in another table.
4) primary key is used to identify a row and it doesnot
allow
null values. It avoids duplication of rows.
whereas foreign key refers to a column or combination of
columns included in the defenition of referential integrity.
referential integrity by completing an association between
two entities.
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