### TODO
- coalesce, date functions now, add_date; string functions rtrim, ltrim, rpad, lpad; math function round
- add pipe | concatenation

- support for order by, offset, limit (allow column name in order by, validate)
- support for uniqueue indexes (primary key)
- support for btree indexes
- support for joining
- add count min and max functions, eg aggregate functions

- add const wherever should be
- PERF in Row::Row(const Row &other), could be more efficient (memory and cpu)
- use references where pointer cannot be nullptr