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I always thought that I suck in SQL but if these are medium to hard then I am not that bad actually.

SQL for Smarties is the book that has proven, without a doubt, I am bad at SQL. https://www.amazon.com/Joe-Celkos-SQL-Smarties-Programming/d...

If you want to get undeniably good with SQL, this is the book.

These are easy enough to do in your head.

Also I would do a lot of them differently. And I don't think the answer to #6 is valid (in T-SQL at least).