Win a copy of Rust Web Development this week in the Other Languages forum!
  • Post Reply Bookmark Topic Watch Topic
  • New Topic
programming forums Java Mobile Certification Databases Caching Books Engineering Micro Controllers OS Languages Paradigms IDEs Build Tools Frameworks Application Servers Open Source This Site Careers Other Pie Elite all forums
this forum made possible by our volunteer staff, including ...
Marshals:
  • Tim Cooke
  • Campbell Ritchie
  • Ron McLeod
  • Liutauras Vilda
  • Jeanne Boyarsky
Sheriffs:
  • Junilu Lacar
  • Rob Spoor
  • Paul Clapham
Saloon Keepers:
  • Tim Holloway
  • Tim Moores
  • Jesse Silverman
  • Stephan van Hulst
  • Carey Brown
Bartenders:
  • Al Hobbs
  • Piet Souris
  • Frits Walraven

Why use a Unique Key when you can use a Primary Key?

 
Greenhorn
Posts: 2
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Hi, this is my first post, and I'm not sure if it should go in this topic or not, but here it goes. I was reading about unique keys and primary keys in Wikipedia, and it seems that a primary key is a special case of a unique key, in that a primary key cannot hold a NULL value.

I was wondering:
1) Why are unique keys called "unique keys"?
2) Why use a unique key when you can use a primary key?

Thanks in advance.
 
Ranch Hand
Posts: 2458
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
A PK is considered to be an unique identifier of the row. It should never be subject to changes. For example the ID of the User.

An UK is considered to be unique thoroughout the whole column. It is not necessarily an identifier of the row as it may be subject to changes. For example the username or email address of the User.
 
Anderson Goldman
Greenhorn
Posts: 2
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Got it. Thank you!
 
Bauke Scholtz
Ranch Hand
Posts: 2458
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
You're welcome.
 
With a little knowledge, a cast iron skillet is non-stick and lasts a lifetime.
reply
    Bookmark Topic Watch Topic
  • New Topic