We have been using something like this based on Blockly in production for over seven years now to build dashboards. GIF demo: https://www.dialogic.nl/wp-content/uploads/2018/02/demo1.gif

Our users (researchers) had no problems learning the concepts of querying but didn't want to be bothered learning SQL syntax - hence we built this (also, our system does quite a bit of magic behind the scenes to allow mixing e.g. CSV data with data from a database, and also allows for things not easily done in SQL, e.g. pivot tables, so it's not just SQL).