geek/talk: Web publishing business discussion - View Single Post - What's the difference between a primary key and a unique key in SQL?

ketul · 08-17-2017, 12:13 AM

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 on Unique-key

08-17-2017, 12:13 AM	#2
ketul Registered User Join Date: Aug 2014 Location: bangalore Posts: 416	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 on Unique-key