Supporting CTE

[jwoertink]

I use a lot of these thing, and always have to drop to raw SQL because of it. It would be great if Avram had it built right in

Here's my initial proposal

schedule_query = <<-SQL
SELECT ...
SQL
UserQuery.new.with_cte(:schedules, as: schedule_query)

Or maybe go the route of Avram::Join with something like Avram::CTE https://github.com/luckyframework/avram/blob/main/src/avram/join.cr

cte = Avram::CTE.new(:schedules) do |io|
  io << "SELECT ... FROM ...."
end

UserQuery.new.with_cte(cte)

I'll have to research a bit more of how many of my raw queries could be converted through this method. I know not all of them, but this could possibly clear up quite a bit.