Mapping columns
After mapping your tables using the Map Tables wizard, you can use the Column Mappings tab in the Table Mappings view to customize what items you want to map to target columns in a subscription.
If you have mapped your tables using any mapping type, then most or all of your target columns are already mapped to source columns that have identical names and attributes. However, using the Columns Mappings tab, you can customize the kind of information you want to map to a target column and populate it with.
Db2 for z/OS: Database defaults, if defined in the target database, will be used automatically during the mapping process if there is no compatible (that is to say, identically named) source column for the target column.