Question

Naming conventions are important, and primary key and foreign key have commonly used and obvious conventions (PK_Table and FK_Table_ReferencedTable, respectively). The IX_Table_Column naming for indexes is also fairly standard.

What about the UNIQUE constraint? Is there a commonly accepted naming convention for this constraint? I’ve seen UK_TableName_Column, UQ_TableName_Column, and someone recommending AX_TableName_Column – I don’t know where that comes from.

I’ve typically used UQ but I don’t particularly like it, and I do not enjoy having to defend my choice of using it against a UK advocate.

I would simply like to see if there is a consensus on the most prevalent naming, or a good reasoning as to why one makes more sense than the others.

Answer 1

My thinking is it isn’t a key: it’s a constraint.

It could be used as a key of course, and uniquely identifies a row, but it isn’t the key.

An example would be that the key is “ThingID”, a surrogate key used in place of ThingName the natural key. You still need to constrain ThingName: it won’t be used as a key though.

I’d also use UQ and UQC (if clustered).

You could use a unique index instead and go for “IXU”. By the logic employed, an index is also a key but only when unique. Otherwise it’s an index. So then we’d start with IK_columnname for unique indexes and IX_columnname for non-unique indexes. Marvellous.

And the only difference between a unique constraint and a unique index is INCLUDE columns.

Edit: Feb 2013. Since SQL Server 2008, indexes can have filters too. Constraints can not

So, it comes down to one of

• stick with UQ as per the rest of the SQL-using planet
• use IK for unique indexes (IKC for clustered too) to be consistent…