Hey Alexander concatenation is done wherever there are common field names between two tables. If the field doesn't exist the value will be null. Concatenation doesn't need key fields(they come into play only in Joins).
Ex:
| A | B | C | D |
|---|
| 1 | US | 123 | 23.4 |
| 2 | CAD | 234 | 3.3 |
| 3 | MEX | 345 | 1.2 |
| 4 | Aus | 456 | 0.9 |
| A | C | Z |
|---|
| 1 | 123 | alpha |
| 2 | 234 | beta |
| 4 | 100 | gamma |
Result after concatenation:
| A | B | C | D | Z |
|---|
| 1 | US | 123 | 23.4 | - |
| 2 | CAD | 234 | 3.3 | - |
| 3 | MEX | 345 | 1.2 | - |
| 4 | Aus | 456 | 0.9 | - |
| 1 | - | 123 | - | alpha |
| 2 | - | 234 | - | beta |
| 4 | - | 100 | - | gamma |
