MySQL之DQL

MySQL之DQL

#查看表的创建过程

MariaDB [test]> show create table student; +---------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Table | Create Table | +---------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | student | CREATE TABLE `student` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT, `name` varchar(20) NOT NULL, `age` tinyint(3) unsigned DEFAULT NULL, `gender` enum('M','F') DEFAULT 'M', PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=47 DEFAULT CHARSET=utf8 | +---------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1 row in set (0.000 sec) MariaDB [test]>

取阴影部分：

#完全左连接剔除学生表里面和老师表有共同之处的部分： MariaDB [hellodb]> select * from students s left outer join teachers t on s.teacherid=t.tid where t.tid is null; +-------+---------------+-----+--------+---------+-----------+------+------+------+--------+ | StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name | Age | Gender | +-------+---------------+-----+--------+---------+-----------+------+------+------+--------+ | 2 | Shi Potian | 22 | M | 1 | 7 | NULL | NULL | NULL | NULL | | 3 | Xie Yanke | 53 | M | 2 | 16 | NULL | NULL | NULL | NULL | | 6 | Shi Qing | 46 | M | 5 | NULL | NULL | NULL | NULL | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | NULL | NULL | NULL | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | NULL | NULL | NULL | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | NULL | NULL | NULL | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | NULL | NULL | NULL | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | NULL | NULL | NULL | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | NULL | NULL | NULL | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | NULL | NULL | NULL | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | NULL | NULL | NULL | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | NULL | NULL | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | NULL | NULL | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+------+------+------+--------+ 22 rows in set (0.000 sec) #左连接落后剔除 teacherid为空的 MariaDB [hellodb]> select * from students s left outer join teachers t on s.teacherid=t.tid where s.teacherid is null; +-------+---------------+-----+--------+---------+-----------+------+------+------+--------+ | StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name | Age | Gender | +-------+---------------+-----+--------+---------+-----------+------+------+------+--------+ | 6 | Shi Qing | 46 | M | 5 | NULL | NULL | NULL | NULL | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | NULL | NULL | NULL | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | NULL | NULL | NULL | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | NULL | NULL | NULL | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | NULL | NULL | NULL | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | NULL | NULL | NULL | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | NULL | NULL | NULL | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | NULL | NULL | NULL | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | NULL | NULL | NULL | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | NULL | NULL | NULL | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | NULL | NULL | NULL | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | NULL | NULL | NULL | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | NULL | NULL | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | NULL | NULL | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+------+------+------+--------+ 20 rows in set (0.000 sec)

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