Answer Posted / ambresh pratap srivastava

primary key is combination of column which uniquely specify a row.A table have at most one primary key. primary key creates Clustered Index.A primary key column allows no row having null value

Unique key can uniquely identify each row in a table and is closely related to super key concept.A unique key comprises a single column or a group of column.A unique key column allows only one row having null value.Unique key creates unclustered Index.

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