Need to know how value populates on a custom field

Hi Experts,

We have a custom field named 'EXTERNAL_CUST_ACCOUNT_ID' in Partner object in CRM application.

We don't find this custom field used in any of the application pages.

This field is referred in column 'EXTN_ATTRIBUTE_NUMBER012' in the table ZPM_PARTNER_PROFILES.

This column has value only for customers (Partners) who are created in ERP module and then migrated to PRM (Partner Relationship Management) module. This column is NULL for all customers who are created directly created in PRM.

Below is the sample query, There are 2 partners given in the IN condition.

Partner Number: PRTL_218032 ⇒ Partner created directly in PRM, so the EXTN_ATTRIBUTE_NUMBER012 column value is NULL