Please start any new threads on our new
site at https://forums.sqlteam.com. We've got lots of great SQL Server
experts to answer whatever question you can come up with.
| Author |
Topic |
|
ravilobo
Master Smack Fu Yak Hacker
1184 Posts |
 Posted - 2008-05-07 : 16:20:28
|
| What is the difference between unqiue constraint and unique index? What are the pros and cons? Are they interchangable?------------------------I think, therefore I am - Rene Descartes |
|
|
sodeep
Master Smack Fu Yak Hacker
7174 Posts |
Posted - 2008-05-07 : 16:26:07
|
| Both are same. |
 |
|
|
tkizer
Almighty SQL Goddess
38200 Posts |
Posted - 2008-05-07 : 16:38:27
|
From SQL Server Books Online:quote:
Creating a unique index guarantees that any attempt to duplicate key values fails. There are no significant differences between creating a UNIQUE constraint and creating a unique index that is independent of a constraint. Data validation occurs in the same manner, and the query optimizer does not differentiate between a unique index created by a constraint or manually created. However, you should create a UNIQUE constraint on the column when data integrity is the objective. This makes the objective of the index clear.
We require that unique constraints are used instead of unique indexes.Tara KizerMicrosoft MVP for Windows Server System - SQL Serverhttp://weblogs.sqlteam.com/tarad/Database maintenance routines:http://weblogs.sqlteam.com/tarad/archive/2004/07/02/1705.aspx |
|
|
|
ravilobo
Master Smack Fu Yak Hacker
1184 Posts |
Posted - 2008-05-07 : 16:41:32
|
| Thanks Tara. Thanks Sodeep.------------------------I think, therefore I am - Rene Descartes |
|
|
|
rmiao
Master Smack Fu Yak Hacker
7266 Posts |
Posted - 2008-05-07 : 16:47:31
|
| Small difference, sql will check with unique constraints before updating data while check unique indexes afterwards. |
|
|
|
|
|
|
Unique constraint/Index