ETL execution sequence
The execution sequence of ETL scripts in Data Warehouse projects should be taken into consideration when writing and ordering the scripts. A proper understanding of the ETL execution order is important for preventing errors, such as those resulting from actions being performed on objects that do not yet exist.
ETL scripts are usually executed in the following order:
| Custom Pre-Loading (Source of data: landing tables) |
| ↓ |
| Mappings (Source of data: landing table) |
| ↓ |
|
Multi Table ETL (Source of data: staging tables) Information note
Whereas it's possible to define a single table ETL in the Multi Table ETL script, the advantage of defining it as a single table ETL script is that it will be able to run in parallel with other tables. |
| ↓ |
| Single Table ETL (Source of data: staging tables) |
| ↓ |
| Post Loading ETL (Source of data: data warehouse tables) |
Within each of the above groups, the scripts are executed according to their numeric order (from lowest to highest), which is set by the user-defined Sequence Number. The execution order of several scripts in a group with the same sequence number will be random.