title: Deciding on a primary key according to value size in SQL Server
body: <p>I want to ask a question to optimize SQL Server performance. Assume I have an entity - say <code>Item</code> - and I must assign a primary key for it. It has columns and two of them are expected to be unique, one of them is expected to be bigger than the other as tens of characters. </p>
  
  <p>How should I decide primary key? </p>
  
  <p>Should one of them be PK, if so which one, or both, or should I create an Identity number as PK? This is important for me because the entity "Item" would have relations with some other entities and I think the complexity of PK would affect the performance of SQL Server queries.</p>