A FieldTransform is not the right place to define variable values
To achieve this you can:
Alternative 1:
- Create variable "number of records"
- Create new transform of type TableLoop with
* Loop source: The extract with 1 column (named "number of records") and 1 row
* Data source: The source which uses this variable anywhere
Alternative 2:
- Create variable "number of records"
- Create new job of type eLoop with
* Loop source: The extract with 1 column (named "number of records") and 1 row
* Execution type/name: A load or job which uses this variable anywhere
Handling of datatypes is a separate topic.