Numerous attempts have been made at visual SQL queries. The problem is learning them doesn't gain you anything over SQL really, and you have now spent your time learning a non-standard way of doing things (MS Access query builder was OK). Better spend your time practising some advanced queries than learning yet another visual tool.
Sorry, I didn't understand your answer. It is very important to understand the complex query in-order to debug or re-engineer. One way is to visualise it as mentioned in the article and convert it to SQL via pipeSQL.
I personally haven't found visual tools made querying any easier, just a new way of doing things - essentially a new syntax. Practising normal SQL and being able to visualize it in my head has been far more use than any visual tools have been to me.