SELECT f.film_id,f.title FROM film f LEFT JOIN film_category fi ON f.film_id=fi.film_id LEFT JOIN category c ON fi.category_id=c.category_id WHERE fi.category_id is NULL
两次左外连接把三个表连到一起
关键: is nuLL 用来判断是否为NULL
SELECT f.film_id,f.title FROM film f LEFT JOIN film_category fi ON f.film_id=fi.film_id LEFT JOIN category c ON fi.category_id=c.category_id WHERE fi.category_id is NULL
两次左外连接把三个表连到一起
关键: is nuLL 用来判断是否为NULL