In Odoo, there’s no direct or automatic way to merge two separate databases into one multi-company database. You’ll need to migrate and consolidate the data.

The recommended approach:

    Set up the target DB — Create the second company under Settings → Companies in your primary database

    Align Chart of Accounts — Map and create matching accounts for the new company before any data import

    Migrate master data — Export Contacts, Products, and Bank Accounts from the source DB and import into the target. Note that Products are global in Odoo — no duplication needed

    Handle shared partners — Don't duplicate common customers/vendors. Link them to both companies via company_ids

    Opening balances — Post a single Opening Journal Entry reflecting the trial balance as of migration date. Avoid migrating full journal entry history

    Open transactions only — Recreate or import only open Sales Orders, Purchase Orders, and Invoices with correct company_id

    Stock — Use Inventory Adjustments to enter opening quantities for the new company