Question
In Segment, does Alias work with Unify?
Product
Twilio Segment
Environment
Segment Console
Answer
The Alias call is not intended for merging profiles within Segment. It is only available as a method that is used for specific destinations to overcome a limitation that is specific to those destinations such as:
Generally, for most destinations, an Identify call is all that is necessary to associate the Anonymous ID with a User ID. However, the destinations above require an extra step to draw that association and that's where the Alias call comes into play. It has a pretty limited use case and is not intended for general purpose mergers of different users in Segment or any other destinations (aside from the ones listed above).
In Unify, profiles are merged based on your Identity Resolution Configuration settings, and it is not possible to influence this process from the 'outside' (aside from changing Identity Resolution settings, of course, but the changes will not be applied retroactively).
For the merge to happen, there have to be some common identifier passed, and the merge should not cause any violations - for instance, if your ID Resolution allows only one user_id, two profiles with different user_id's can never be merged.
Additional Information
More resources on Identity Resolution below: