Table schema:
CREATE TABLE table_name_18 (total_cargo__metric_tonnes_ INTEGER, code__iata_icao_ VARCHAR, rank VARCHAR)

Question: What is the highest total cargo of an airport ranked larger than 19 with a code of BKK/VTBS?
SQL: SELECT MAX(total_cargo__metric_tonnes_) FROM table_name_18 WHERE code__iata_icao_ = "bkk/vtbs" AND rank > 19