Choose a unique identifier field for a query layer

All layers in ArcGIS need a unique identifier. Therefore, your query layer must contain a unique identifier.

In most cases, though, you create query layers to access feature classes and tables in a database. It is standard practice for database tables to contain a unique identifier field; therefore, your database tables will likely already contain a field you can use as a unique identifier.

To be used as a unique identifier in ArcGIS, a field must be not null, contain unique values, and be one of the following data types:

• Integer (positive values only)
• String
• GUID
• Date

Since the value in the unique identifier field uniquely identifies a row or feature object within ArcGIS, values in that field must always be unique and not null. It is your responsibility to guarantee that values in this field meet this requirement.

Note:

You will receive an error if ArcGIS encounters a null value, but ArcGIS does not enforce the uniqueness of values in the unique identifier field used in a query layer or database table. If ArcGIS encounters a nonunique value, no error is returned; however, you may see inconsistent results in selection sets or other queries in ArcGIS.