I want know that data migration tool working with fresh database or with already exist values in Magento2.
Always use a fresh database to migrate from Magento 1 to Magento 2.
If you migrate it with already existing database then highly probability to conflict database table id and it is always through an error.
You can not migrate 100% data in the existing database.
You can do the delta migration process with the same M2 database after the first migration process.