Comparison key is used to determine which rows correspond to each other. You can choose suitable constraints for comparison or specify custom comparison keys. dbForge Data Compare for Oracle can select comparison key automatically if tables have matching primary key or unique constraint.
To choose a constraint pair, click the down arrow button in the Comparison Key column on the Mapping page of the Data Comparison wizard and select the constraint pair you need.
To set a custom comparison key, click the down arrow button in the Comparison Key column on the Mapping page of the Data Comparison wizard and select <Custom>. Then, in the Column Mapping dialog box that appears, select checkboxes in the Key column to add columns to the comparison key.
Note that you can set a custom comparison key or choose the needed constraint pair directly in the Comparison Key drop-down list of the Column Mapping dialog box.
Actual document look may slightly vary from the above image depending on the product you use.