Double-click a field in the table to select it as part of the result. It will appear in the lower Selection window.

tj-selected-columns

Alias
It defines an alias for the column, to rename the column in the result.

Aggregate Function
It define an aggregate function. Following options are available:

Aggregat-function description
avg average
count quantity
max maximum
min minimum
sum amount, total

If you select an aggregate function, an Alias must be defined.

Check the following example, that counts the number of description languages of each material.

tj-aggregate-count

On the right side you have the options to move up, move down or delete the fields.