Question 19Differentiate between Primary key and Unique constraints.

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Primary keyUnique constraintsA Primary key is a set of one or more attributes/fields which uniquely identifies a tuple/row in a table.UNIQUE constraint ensures that no two rows have the same value in the specified column(s).Primary Keys do not allow NULL values.Unique Constraint allows NULL values.There can be only one Primary Key in a table.Multiple Unique Constraints can exist in a table.

Primary key	Unique constraints
A Primary key is a set of one or more attributes/fields which uniquely identifies a tuple/row in a table.	UNIQUE constraint ensures that no two rows have the same value in the specified column(s).
Primary Keys do not allow NULL values.	Unique Constraint allows NULL values.
There can be only one Primary Key in a table.	Multiple Unique Constraints can exist in a table.

Relational Database and SQL — Question 26

Question 19