替换中的前缀wp_users 和wp_usermeta 使用的表名称
在开始删除用户之前，备份两个表中的数据。

DELETE u FROM wp_users u
  LEFT JOIN wp_usermeta um1 ON u.id = um1.user_id AND um1.meta_key = \'first_name\'
  LEFT JOIN wp_usermeta um2 ON u.id = um2.user_id AND um2.meta_key = \'last_name\'
WHERE (um1.meta_value IS NULL OR CHAR_LENGTH(um1.meta_value) = 0)
  AND (um2.meta_value IS NULL OR CHAR_LENGTH(um2.meta_value) = 0);

DELETE um FROM wp_usermeta um
  LEFT JOIN wp_users u ON u.id = um.user_id 
WHERE u.id IS NULL;