MySQL - 选择全部除了此表中的内容

Question

我想要选择用户尚未拥有的所有图像.

我有三个表:user,image,和user_image:

• _user(id,user,pass)
• _image(id,data)
• _user_image(id,user_id,image_id)

Answer 1

运用 LEFT JOIN/IS NULL

   SELECT DISTINCT
          i.data
     FROM IMAGE i
     JOIN USER_IMAGE ui ON ui.image_id = i.id
LEFT JOIN USER u ON u.id = ui.user_id
                AND u.user = ?
    WHERE u.id IS NULL

运用 NOT IN

SELECT DISTINCT
       i.data
  FROM IMAGE i
  JOIN USER_IMAGE ui ON ui.image_id = i.id
 WHERE ui.user_id NOT IN (SELECT u.id
                            FROM USER u
                           WHERE u.user = ?)

运用 NOT EXISTS

SELECT DISTINCT
       i.data
  FROM IMAGE i
  JOIN USER_IMAGE ui ON ui.image_id = i.id
 WHERE NOT EXISTS(SELECT NULL
                    FROM USER u
                   WHERE u.id = ui.user_id
                     AND u.user = ?)

性能:

的LEFT JOIN/IS NULL和NOT IN提供相当的性能-的NOT EXISTS是〜30%的效率低. 有关详细信息,请参阅本.