Naming convention for unique constraint

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.

My naming convention for indices and constraints:

Index/Constraint Type	Naming Convention
Primary key	<table-name>_PK
Unique index/constraint	<table-name>_AK{xx}
Non-Unique index	<table-name>_IX{xx}
Check constraint	<table-name>_CK{xx}
Default constraint	<table-name>_DF{xx}
Foreign key constraint	<table-name>_FK{xx}

Where {xx} is a 2-digit sequence number, starting at 01 for each constraint type per table. Primary key doesn't get a sequence number since there can be only one. The 2-char alpha suffix meanings are:

Suffix	Meaning
PK	Primary Key
AK	Alternate Key
FK	Foreign Key
IX	IndeX
CK	ChecK
DF	DeFault

I generally want to group metadata/system catalog data by the controlling object rather than by object type.

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...

I use UQ. The K in UK makes me think of K as it's used in PK and FK. Well, after I think of United Kingdom anyways; ironic that this should be a prefix for UNIQUE when UK brings up so many other associations =)