> ## Documentation Index > Fetch the complete documentation index at: https://www.integrate.io/docs/llms.txt > Use this file to discover all available pages before exploring further. # ELT/CDC: Custom Primary Key Feature > Use the custom primary key feature to sync tables without a primary key in Integrate.io ELT & CDC. Define surrogate keys for keyless tables. ### Prerequisite: The table must have a unique key using NOT NULL columns. The unique key will work as the primary key for sync.  This will only be set on the destination for Integrate.io ELT & CDC Sync. ### Getting Started Modify the column of your table to set a custom PK Table column list with option to set a custom primary key Select a column(s) that has a **unique key** and is **NOT NULL**. Selecting a unique NOT NULL column as the custom primary key Once selected, hit **Save** Custom primary key selected with Save button Click **Continue to Sync Settings** to start the replication. Continue to Sync Settings button to start replication