TODO

• date functions - now, add_date...
• string functions rtrim, ltrim, rpad, lpad
• round function
• add pipe | concatenation
• support for order by, offset, limit (allow column name in order by, validate)
• command line interface
• support for uniqueue indexes (primary key)
• support for btree indexes
• 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