Query Builder queries must have an aggregate function.

[ebb-tide]

All new query builder queries start with the 'mean' aggregate function applied by default.
Aggregate functions can not be deselected.
There is no restriction on scripts that can be created with the script editor.
If a user's preexisting query (in a dashboard) does not contain any aggregate functions, when they attempt to view/edit their query in the query builder the UI drops them in to the script editor instead of editing their existing query.