A 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, it will be used for ID generation.

• 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.

It is preferred that the table contain rows of like data type.