All layers in ArcGIS—including query layers, layers from geodatabases, and layers from databases—require a unique identifier.
If you define a query layer on a single geodatabase table or feature class, use the object ID field as the unique identifier field.
In most cases, though, you create query layers to access feature classes and tables in a database or drag a database layer directly into a map in an ArcGIS Desktop client. It is standard practice for database tables to contain a unique identifier field; therefore, your database tables likely already contain a field you can use as a unique identifier. If so, ArcGIS Pro will detect the qualifying field and set it as the unique identifier.
To use a field as a unique identifier in ArcGIS desktop apps, the field must be not null, contain unique values, and be one of the following data types:
- Integer (positive values only)
- String
- GUID
- Date
Values in the field must always be unique and not null. It is your responsibility to guarantee that values in this field meet these requirements.
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.
If you want to publish the query layer in a feature layer (a feature service) that references the registered data store, the ID must be a single, not null, unique, autoincrementing integer field.
If a qualifying field is present, ArcGIS sets the first not-null field it finds as the unique identifier field by default when you drag a database table from the Catalog pane and place it in the map or validate a query layer definition. This is often an adequate value to use as the unique identifier field, but you can choose another qualifying field or fields from the Unique Identifier Field(s) list to be used instead. If you want to choose your own unique identifier, you can modify the query layer.