cstm TABLE and fields where is the data stored?

[casqldba]

I understand that all custom fields are stored in a custom table (i.e. opportunities_cstm) I did the migration step in studio to move the custom fields to the module so that they show to all users. But I have a question. If the custom fields are not in the opportunities table how does the associated data stored in the custom fields/table stay in sync. I saw one ID field in the custom table but I don't see how that gets associated with the oppportunities table. Am I missing a step? I don't think I need to manually move the fields to the table. But I want to make sure all the data is one place. I also want it to carry over the same data stored in the custom fields to other modules. I shouldn't need to create the same custom fields in each module that I want it to appear; it wouldnt be in sync.I want to be able to report on one table. Thanks in advance.

[eggsurplus]

Custom fields pertain only to that module that it's created for. So a custom field for opportunities would be in opportunities_cstm. An accounts custom field would pull from a separate table (accounts_cstm). The id_c field in the _cstm tables link directly to the id field of the associated table. So id_c in opportunities_cstm is the same value as it's id counterpart in opportunities.

Hope that makes sense.