Compose automap is a handy button to press for 99% of landing to DW mappings. There are usually a few columns that have to be mapped by hand though, and once mapped, should stick that way unless prompted to replace them. Full scenario (actually encountered):
1. Landing has fields "F1" and "F1_ALT".
2. DW has field "F1_ALT".
3. Desired mapping: F1->F1_ALT done manually.
4. Additional columns added later to landing and DW.
5. Automap used to map new columns. Result: Previous manual mapping silently replaced with F1_ALT->F1_ALT.
Automap should recognize different scenarios:
- Not mapped - automap ok
- Mapped like to like - no automap change needed
- Mapped manually - prompt user - ideally let user choose to preserve existing mappings or replace on a field level or for all changes.
