Data Compare for SQL Server allows you to map columns with non-equal names. You may map columns with different types, however this may result in data truncation, rounding, and errors during synchronization for certain types. If such a situation is possible, a warning icon Caution appears in the Target Column column of the Select columns for comparison grid. If the columns are not compatible and cannot be compared, the Error icon appears near this column. For more information about types compatibility and mapping warnings, see the Mapping Warnings and Types Compatibility topics.
For customizing column mapping the Column Mapping dialog box is used. To open it, click the Ellipsis button in the Columns in Comparison column on the Mapping page of the Data Comparison wizard.
Actual document look may slightly vary from the above image depending on the product you use.
If you want to remap already mapped columns, you should unmap them first.
Click the corresponding cell in the Target Column column and choose None.
Click the corresponding cell in the Target Column column and choose the column you need.