sql - Fill with @row_number based on group field in QGIS 3?

Is there a way to fill the table with a row number so that count will restart as new group (identified by a separate column) starts? As a result, "row number" column will restart the count when the new attribute value for a group is found, and will produce row number (1,2,3 etc.) record within this group.

This post on stack overflow seems to answer my question, but SQL in QGIS does not allow such statements (DENSE_RANK) (or it does but I don't know how?).

Answer

Do you need to use a field calculator? If not, the "Add autoincremental field" algorithm from the processing toolbox does what you want.