From looking at AdventureWorks2008 database (HumanResources.Employee table) it seems that Microsoft uses this convention for index prefixes:

PK - Primary Key

IX - Non-Unique Index

AK - Unique Index

Does anyone know what A and K stand for in AK?

• Edited by JoeSchmoe115 Tuesday, July 26, 2011 6:48 PM

A Stand for Alternate as Unique Constraint can sometime also be referred to as Alternate Key Constraint.

taken form  http://en.wikipedia.org/wiki/Unique_key

It is commonplace in SQL databases to declare a single primary key, the most important unique key. However, there could be further unique keys that could serve the same purpose. These should be marked as 'unique' keys. This is done to prevent incorrect data from entering a table (a duplicate entry is not valid in a unique column) and to make the database more complete and useful. These could be called alternate keys

When you create unique constraint (or alternate key constraint) behind the scene SQL server will create unique index so naming convention uses AK

• Proposed as answer by Naomi NEditor Tuesday, July 26, 2011 6:42 PM
• Marked as answer by JoeSchmoe115 Tuesday, July 26, 2011 6:47 PM
• Edited by Chirag Shah Tuesday, July 26, 2011 7:04 PM

A Stand for Alternate as Unique Constraint can sometime also be referred to as Alternate Key Constraint.

taken form  http://en.wikipedia.org/wiki/Unique_key

It is commonplace in SQL databases to declare a single primary key, the most important unique key. However, there could be further unique keys that could serve the same purpose. These should be marked as 'unique' keys. This is done to prevent incorrect data from entering a table (a duplicate entry is not valid in a unique column) and to make the database more complete and useful. These could be called alternate keys

When you create unique constraint (or alternate key constraint) behind the scene SQL server will create unique index so naming convention uses AX

Makes sense. And of course I made a mistake in OP - AX should have been AK (Alternate Key), will fix it now

any idea for this,

https://social.technet.microsoft.com/Forums/en-US/e48e9c08-4ad3-4dee-a0fc-44cf3885217d/microsoft-recommended-index-naming-standard-sql-server?forum=databasedesign