Is there this possibility (Group by) in the Query Editor (by clicking somewhere)?
Example: I pick a dimension (a country) and a measure (Sales) and I want the output to be the SUM(Sales) by Country
Yes, it’s possible. Right-click a column and pick aggregation type. If at least 1 column is aggregated, the rest of the columns will be used for grouping. Aggregated columns are indicated with a blue line.
Also, when 1 or more columns are aggregated, their values can be post-filtererd, i.e. filtered AFTER aggregation. For this, switch to the Post-filter condition tab, and specify a filtering condition just like in the regular Filter tab.