Hi
I've 13+ years of experience in Software Development, Currently working as a Solution Architect with ASIA's largest DTH company. During these years I've been working with SQL/MY SQL, I'm good at query tuning & indexes.
Regarding the writing question related to SQL queries, I can perfectly write questions based on your expectation, for instance, Questions can be written to target Novice, Intermediate or for the expert user group.
Time depends on the number of tables your ER diagram have.
Regards
Brijesh Mathur