Question

Difference between primary key and unique key and foreign key

Answer 1

Hey mate here is your answer:
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Primary key is a field or set of fields that uniquely identifies each record in a table , it doesn't contains any duplicate data.

When creating a query in Microsoft Access , you might want to return only distinct or unique values , in such cases unique key is used.

Foreign key is defined in second table , but it refers to the primary key or unique key in first table.
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HOPE IT HELPS YOU MATE!

Answer 2

primary key
1)primary key cannot have a null value.
2)each table have only one primary key.
3)primary key us related to another table as a foreign key
4) we can define primary key constraint or temporary table and table variable.

unique key
1) unique constraint may have a null value.
2)each table can more than one unique constraint.
3)by default,unique key is a unique non clustered index.
4) unique constraint cannot be related with another table as a foreign key.

foreign key
1) foreign key is a field in the table that is primary key in other table.
2)we can have more than one foreign key in a table.
3)we cannot define foreign key constraint on temporary table or table variable.
4)we can delete the foreign key value from the child table even though that refers to the primary key of the parent table.