Group

Partitions the rows into groups and applies a pipeline to each of the groups.

group {key_columns} (pipeline)

The partitioning of groups are determined by the key_columns (first argument).

The most conventional use of group is with aggregate:

from employees
group {title, country} (
  aggregate {
    average salary,
    ct = count salary
  }
)

In concept, a transform in context of a group does the same transformation to the group as it would to the table — for example finding the employee who joined first across the whole table:

from employees
sort join_date
take 1

To find the employee who joined first in each department, it's exactly the same pipeline, but within a group expression:

from employees
group role (
  sort join_date  # taken from above
  take 1
)