Originally posted by ronnie
Does this mean that a unique constraint does not create an Index. (but primary key constraint does)
No.

Both UK and PK constraint must have underlying index to enforce uniqueness. So if the appropriate index (either unique or nonunique) does not allready exist when you create the PK or UK constraint the unique index will be created automaticaly when you create the constraint.

The mayor differences between UK and Pk are:
- there could only be one PK per table, while there could be many UK per table
- for PK, all columns included in the key must be NOt NULL, while UK can incorporate also nullable columns