Select stmt - Userexit - CDB service

Hi,

We have a custom table which gets regularly updated from TSM laptops. In this process only few fields from laptop should get updated to table as we are getting other fields values from other system and they should not be overwritten by the value in laptop.

Am trying to write a select stmt in after CDB userexit to get the value from custom table before updating the table and modify the field with the value in custom table and update the table so that the value from laptop is not overwritten. But the select stmt is not retrieving the value from custom table.

Could you please suggest a solution to achieve this.

Regards,

Sandhya