More details about "Why functions and column-orientation" (as opposed to sets) can be found in [2]. Shortly, problems with set-orientation and SQL are because producing sets is not what we frequently need - we need new columns and not new table. And hence applying set operations is a kind of workaround due the absence of column operations.
This approach is implemented in the Prosto data processing toolkit [0] and Column-SQL[1] is a syntactic way to define its operations.
[0] https://github.com/asavinov/prosto Prosto is a data processing toolkit - an alternative to map-reduce and join-groupby
[1] https://prosto.readthedocs.io/en/latest/text/column-sql.html Column-SQL (work in progress)
[2] https://prosto.readthedocs.io/en/latest/text/why.html Why functions and column-orientation?