CREATE TABLE tourist_attractions (tourist_attraction_id NUMBER, attraction_type_code CLOB, location_id NUMBER, how_to_get_there CLOB, name CLOB, description CLOB, opening_hours CLOB, other_details CLOB)
CREATE TABLE locations (location_id NUMBER, location_name CLOB, address CLOB, other_details CLOB)
CREATE TABLE visitors (tourist_id NUMBER, tourist_details CLOB)
CREATE TABLE ref_attraction_types (attraction_type_code CLOB, attraction_type_description CLOB)
CREATE TABLE theme_parks (theme_park_id NUMBER, theme_park_details CLOB)
CREATE TABLE staff (staff_id NUMBER, tourist_attraction_id NUMBER, name CLOB, other_details CLOB)
CREATE TABLE hotels (hotel_id NUMBER, star_rating_code CLOB, pets_allowed_yn CLOB, price_range NUMBER, other_hotel_details CLOB)
CREATE TABLE shops (shop_id NUMBER, shop_details CLOB)
CREATE TABLE tourist_attraction_features (tourist_attraction_id NUMBER, feature_id NUMBER)
CREATE TABLE street_markets (market_id NUMBER, market_details CLOB)
CREATE TABLE ref_hotel_star_ratings (star_rating_code CLOB, star_rating_description CLOB)
CREATE TABLE features (feature_id NUMBER, feature_details CLOB)
CREATE TABLE photos (photo_id NUMBER, tourist_attraction_id NUMBER, name CLOB, description CLOB, filename CLOB, other_details CLOB)
CREATE TABLE visits (visit_id NUMBER, tourist_attraction_id NUMBER, tourist_id NUMBER, visit_date TIME, visit_details CLOB)
CREATE TABLE royal_family (royal_family_id NUMBER, royal_family_details CLOB)
CREATE TABLE museums (museum_id NUMBER, museum_details CLOB)

What are the distinct visit dates?
SELECT DISTINCT visit_date FROM visits
SELECT DISTINCT "visit_date" FROM "visits"