CREATE TABLE "ships_operated_by_zeeland_steamship_comp" (
  "ship_s_name" text,
  "date_entered_service" text,
  "date_withdrawn" text,
  "tonnage" real,
  "type_of_ship" text
);

Question: what is the sum of tonnage when the type of ship is twin screw ro-ro motorship and the date entered service is 11 february 1983?
SQL: SELECT SUM("tonnage") FROM "ships_operated_by_zeeland_steamship_comp" WHERE "type_of_ship"='twin screw ro-ro motorship' AND "date_entered_service"='11 february 1983';

Question: what is the ships name that is a twin screw ro-ro motorship and entered service on 11 february 1983?
SQL: SELECT "ship_s_name" FROM "ships_operated_by_zeeland_steamship_comp" WHERE "type_of_ship"='twin screw ro-ro motorship' AND "date_entered_service"='11 february 1983';

Question: what is the least tonnage for the ship(s) that entered service on 11 february 1983?
SQL: SELECT MIN("tonnage") FROM "ships_operated_by_zeeland_steamship_comp" WHERE "date_entered_service"='11 february 1983';

Question: what is the name of the ship that was withdrawn from service on 25 march 1986?
SQL: SELECT "ship_s_name" FROM "ships_operated_by_zeeland_steamship_comp" WHERE "date_withdrawn"='25 march 1986';

Question: what is the tonnage of the ship koningin juliana?
SQL: SELECT "tonnage" FROM "ships_operated_by_zeeland_steamship_comp" WHERE "ship_s_name"='koningin juliana';