An SQL Server table should have a primary key defined to ensure rows can be identified uniquely. The preferred mechanism is to define the primary key column as IDENTITY.

• If the primary key column has an IDENTITY specification, then the IDENTITY generator will be used to populate this column with a unique value.
• If the primary key does not have an IDENTITY specification then:
  • For a numeric primary key OpenCities Map will query for the maximum value and increment that by one when adding a new record.
  • For other column types OpenCities Map will attempt to store the UUID that XFM uses internally.