I became much better in Sql over the recent two weeks. I learned a few important things that just blocked me from being able to write Sql before.
The main thing I needed to change mindset from programming in java style my brain just couldn't fit the Sql mindset.
1. Think of new columns as variables.
2. Think of new tables as variables.
3. Think of Sql as functions take some input transform put output in a new column (variable) or new table. And less like a magical big bulk of Sql to pull many data many tables join and output, no, split to functions, to smaller Sql just like functions.
4. When writing Sql try to think first as a sequence of functions, doThis, doThat, doThis, then transform each of them to a small Sql query, each result is in a new column, or a new table.
With the above steps I can start thinking about how to write Sql that I need, before getting the above concept I had a block, I just could not get how to approach Sql.