Summary: You can add an expression when connecting to a relational database as part of an ETL (Extract, Transform and Load) process. Expressions allows you to transform existing fields or create new ones based on a formula.
If you need to transform existing fields or add additional ones, you can create an expression as part of the transformations step when connecting to a dataset. This is useful in cases where you need to do some data cleansing on the retrieved data, for example. Alternatively, you can always create a calculated column after the data is retrieved.
To add an expression, do the following
1- Click on “Add new expression”
2- in the expression popup, you will have two options
A. To amend on an existing field, select the field from the list, then type the formula to transform the field. Note that since the expression will be directly applied to the data source when loading the data, the filter expression would need to be in the same SQL language as the source database.
B. To create a new field, first select “New Column” and then type the new field name, and the formula.
3- Once the expression is saved it will show in the expressions list on the transformation page:
4- You can repeat the steps above to create multiple expressions