Question

Define Primary Key. How it is different from Unique Key.

Answer 1

Primary Key is used to identify a row (record) in a table, whereas Unique-key is to prevent duplicate values in a column (with the exception of a null entry).

2. Indexing: By default SQL-engine creates Clustered Index on primary-key if not exists and Non-Clustered Index onUnique-key.

Answer 2

A primary key is defined as a key or database column which uniquely identifies each row in a database table.

Key Difference: A primary key cannot allow null and can only be created once in a table. A unique key allows null and can be created multiple times in a table. The keys play an important part when it comes to storing and retrieving data.

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