mysql多表查询、子查询
2015-06-05 10:25
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mysql> USE hellodb Database changed mysql> SHOW TABLES; +-------------------+ | Tables_in_hellodb | +-------------------+ | classes | | coc | | courses | | scores | | students | | teachers | | toc | +-------------------+ 7 rows in set (0.00 sec) mysql> mysql> SELECT * FROM students; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+ 25 rows in set (0.00 sec) mysql> SELECT * FROM classes; +---------+----------------+----------+ | ClassID | Class | NumOfStu | +---------+----------------+----------+ | 1 | Shaolin Pai | 10 | | 2 | Emei Pai | 7 | | 3 | QingCheng Pai | 11 | | 4 | Wudang Pai | 12 | | 5 | Riyue Shenjiao | 31 | | 6 | Lianshan Pai | 27 | | 7 | Ming Jiao | 27 | | 8 | Xiaoyao Pai | 15 | +---------+----------------+----------+ 8 rows in set (0.00 sec) mysql> SELECT * FROM students,classes; +-------+---------------+-----+--------+---------+-----------+---------+----------------+----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | ClassID | Class | NumOfStu | +-------+---------------+-----+--------+---------+-----------+---------+----------------+----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 1 | Shaolin Pai | 10 | | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 2 | Emei Pai | 7 | | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 3 | QingCheng Pai | 11 | | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 4 | Wudang Pai | 12 | | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 5 | Riyue Shenjiao | 31 | | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 6 | Lianshan Pai | 27 | | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 7 | Ming Jiao | 27 | | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 8 | Xiaoyao Pai | 15 | | 2 | Shi Potian | 22 | M | 1 | 7 | 1 | Shaolin Pai | 10 | | 2 | Shi Potian | 22 | M | 1 | 7 | 2 | Emei Pai | 7 | | 2 | Shi Potian | 22 | M | 1 | 7 | 3 | QingCheng Pai | 11 | | 2 | Shi Potian | 22 | M | 1 | 7 | 4 | Wudang Pai | 12 | | 2 | Shi Potian | 22 | M | 1 | 7 | 5 | Riyue Shenjiao | 31 | | 2 | Shi Potian | 22 | M | 1 | 7 | 6 | Lianshan Pai | 27 | | 2 | Shi Potian | 22 | M | 1 | 7 | 7 | Ming Jiao | 27 | | 2 | Shi Potian | 22 | M | 1 | 7 | 8 | Xiaoyao Pai | 15 | | 3 | Xie Yanke | 53 | M | 2 | 16 | 1 | Shaolin Pai | 10 | | 3 | Xie Yanke | 53 | M | 2 | 16 | 2 | Emei Pai | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | 3 | QingCheng Pai | 11 | | 3 | Xie Yanke | 53 | M | 2 | 16 | 4 | Wudang Pai | 12 | | 3 | Xie Yanke | 53 | M | 2 | 16 | 5 | Riyue Shenjiao | 31 | | 3 | Xie Yanke | 53 | M | 2 | 16 | 6 | Lianshan Pai | 27 | | 3 | Xie Yanke | 53 | M | 2 | 16 | 7 | Ming Jiao | 27 | | 3 | Xie Yanke | 53 | M | 2 | 16 | 8 | Xiaoyao Pai | 15 | | 4 | Ding Dian | 32 | M | 4 | 4 | 1 | Shaolin Pai | 10 | | 4 | Ding Dian | 32 | M | 4 | 4 | 2 | Emei Pai | 7 | | 4 | Ding Dian | 32 | M | 4 | 4 | 3 | QingCheng Pai | 11 | | 4 | Ding Dian | 32 | M | 4 | 4 | 4 | Wudang Pai | 12 | | 4 | Ding Dian | 32 | M | 4 | 4 | 5 | Riyue Shenjiao | 31 | | 4 | Ding Dian | 32 | M | 4 | 4 | 6 | Lianshan Pai | 27 | | 4 | Ding Dian | 32 | M | 4 | 4 | 7 | Ming Jiao | 27 | | 4 | Ding Dian | 32 | M | 4 | 4 | 8 | Xiaoyao Pai | 15 | | 5 | Yu Yutong | 26 | M | 3 | 1 | 1 | Shaolin Pai | 10 | | 5 | Yu Yutong | 26 | M | 3 | 1 | 2 | Emei Pai | 7 | | 5 | Yu Yutong | 26 | M | 3 | 1 | 3 | QingCheng Pai | 11 | | 5 | Yu Yutong | 26 | M | 3 | 1 | 4 | Wudang Pai | 12 | | 5 | Yu Yutong | 26 | M | 3 | 1 | 5 | Riyue Shenjiao | 31 | | 5 | Yu Yutong | 26 | M | 3 | 1 | 6 | Lianshan Pai | 27 | | 5 | Yu Yutong | 26 | M | 3 | 1 | 7 | Ming Jiao | 27 | | 5 | Yu Yutong | 26 | M | 3 | 1 | 8 | Xiaoyao Pai | 15 | | 6 | Shi Qing | 46 | M | 5 | NULL | 1 | Shaolin Pai | 10 | | 6 | Shi Qing | 46 | M | 5 | NULL | 2 | Emei Pai | 7 | | 6 | Shi Qing | 46 | M | 5 | NULL | 3 | QingCheng Pai | 11 | | 6 | Shi Qing | 46 | M | 5 | NULL | 4 | Wudang Pai | 12 | | 6 | Shi Qing | 46 | M | 5 | NULL | 5 | Riyue Shenjiao | 31 | | 6 | Shi Qing | 46 | M | 5 | NULL | 6 | Lianshan Pai | 27 | | 6 | Shi Qing | 46 | M | 5 | NULL | 7 | Ming Jiao | 27 | | 6 | Shi Qing | 46 | M | 5 | NULL | 8 | Xiaoyao Pai | 15 | | 7 | Xi Ren | 19 | F | 3 | NULL | 1 | Shaolin Pai | 10 | | 7 | Xi Ren | 19 | F | 3 | NULL | 2 | Emei Pai | 7 | | 7 | Xi Ren | 19 | F | 3 | NULL | 3 | QingCheng Pai | 11 | | 7 | Xi Ren | 19 | F | 3 | NULL | 4 | Wudang Pai | 12 | | 7 | Xi Ren | 19 | F | 3 | NULL | 5 | Riyue Shenjiao | 31 | | 7 | Xi Ren | 19 | F | 3 | NULL | 6 | Lianshan Pai | 27 | | 7 | Xi Ren | 19 | F | 3 | NULL | 7 | Ming Jiao | 27 | | 7 | Xi Ren | 19 | F | 3 | NULL | 8 | Xiaoyao Pai | 15 | | 8 | Lin Daiyu | 17 | F | 7 | NULL | 1 | Shaolin Pai | 10 | | 8 | Lin Daiyu | 17 | F | 7 | NULL | 2 | Emei Pai | 7 | | 8 | Lin Daiyu | 17 | F | 7 | NULL | 3 | QingCheng Pai | 11 | | 8 | Lin Daiyu | 17 | F | 7 | NULL | 4 | Wudang Pai | 12 | | 8 | Lin Daiyu | 17 | F | 7 | NULL | 5 | Riyue Shenjiao | 31 | | 8 | Lin Daiyu | 17 | F | 7 | NULL | 6 | Lianshan Pai | 27 | | 8 | Lin Daiyu | 17 | F | 7 | NULL | 7 | Ming Jiao | 27 | | 8 | Lin Daiyu | 17 | F | 7 | NULL | 8 | Xiaoyao Pai | 15 | | 9 | Ren Yingying | 20 | F | 6 | NULL | 1 | Shaolin Pai | 10 | | 9 | Ren Yingying | 20 | F | 6 | NULL | 2 | Emei Pai | 7 | | 9 | Ren Yingying | 20 | F | 6 | NULL | 3 | QingCheng Pai | 11 | | 9 | Ren Yingying | 20 | F | 6 | NULL | 4 | Wudang Pai | 12 | | 9 | Ren Yingying | 20 | F | 6 | NULL | 5 | Riyue Shenjiao | 31 | | 9 | Ren Yingying | 20 | F | 6 | NULL | 6 | Lianshan Pai | 27 | | 9 | Ren Yingying | 20 | F | 6 | NULL | 7 | Ming Jiao | 27 | | 9 | Ren Yingying | 20 | F | 6 | NULL | 8 | Xiaoyao Pai | 15 | | 10 | Yue Lingshan | 19 | F | 3 | NULL | 1 | Shaolin Pai | 10 | | 10 | Yue Lingshan | 19 | F | 3 | NULL | 2 | Emei Pai | 7 | | 10 | Yue Lingshan | 19 | F | 3 | NULL | 3 | QingCheng Pai | 11 | | 10 | Yue Lingshan | 19 | F | 3 | NULL | 4 | Wudang Pai | 12 | | 10 | Yue Lingshan | 19 | F | 3 | NULL | 5 | Riyue Shenjiao | 31 | | 10 | Yue Lingshan | 19 | F | 3 | NULL | 6 | Lianshan Pai | 27 | | 10 | Yue Lingshan | 19 | F | 3 | NULL | 7 | Ming Jiao | 27 | | 10 | Yue Lingshan | 19 | F | 3 | NULL | 8 | Xiaoyao Pai | 15 | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | 1 | Shaolin Pai | 10 | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | 2 | Emei Pai | 7 | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | 3 | QingCheng Pai | 11 | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | 4 | Wudang Pai | 12 | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | 5 | Riyue Shenjiao | 31 | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | 6 | Lianshan Pai | 27 | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | 7 | Ming Jiao | 27 | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | 8 | Xiaoyao Pai | 15 | | 12 | Wen Qingqing | 19 | F | 1 | NULL | 1 | Shaolin Pai | 10 | | 12 | Wen Qingqing | 19 | F | 1 | NULL | 2 | Emei Pai | 7 | | 12 | Wen Qingqing | 19 | F | 1 | NULL | 3 | QingCheng Pai | 11 | | 12 | Wen Qingqing | 19 | F | 1 | NULL | 4 | Wudang Pai | 12 | | 12 | Wen Qingqing | 19 | F | 1 | NULL | 5 | Riyue Shenjiao | 31 | | 12 | Wen Qingqing | 19 | F | 1 | NULL | 6 | Lianshan Pai | 27 | | 12 | Wen Qingqing | 19 | F | 1 | NULL | 7 | Ming Jiao | 27 | | 12 | Wen Qingqing | 19 | F | 1 | NULL | 8 | Xiaoyao Pai | 15 | | 13 | Tian Boguang | 33 | M | 2 | NULL | 1 | Shaolin Pai | 10 | | 13 | Tian Boguang | 33 | M | 2 | NULL | 2 | Emei Pai | 7 | | 13 | Tian Boguang | 33 | M | 2 | NULL | 3 | QingCheng Pai | 11 | | 13 | Tian Boguang | 33 | M | 2 | NULL | 4 | Wudang Pai | 12 | | 13 | Tian Boguang | 33 | M | 2 | NULL | 5 | Riyue Shenjiao | 31 | | 13 | Tian Boguang | 33 | M | 2 | NULL | 6 | Lianshan Pai | 27 | | 13 | Tian Boguang | 33 | M | 2 | NULL | 7 | Ming Jiao | 27 | | 13 | Tian Boguang | 33 | M | 2 | NULL | 8 | Xiaoyao Pai | 15 | | 14 | Lu Wushuang | 17 | F | 3 | NULL | 1 | Shaolin Pai | 10 | | 14 | Lu Wushuang | 17 | F | 3 | NULL | 2 | Emei Pai | 7 | | 14 | Lu Wushuang | 17 | F | 3 | NULL | 3 | QingCheng Pai | 11 | | 14 | Lu Wushuang | 17 | F | 3 | NULL | 4 | Wudang Pai | 12 | | 14 | Lu Wushuang | 17 | F | 3 | NULL | 5 | Riyue Shenjiao | 31 | | 14 | Lu Wushuang | 17 | F | 3 | NULL | 6 | Lianshan Pai | 27 | | 14 | Lu Wushuang | 17 | F | 3 | NULL | 7 | Ming Jiao | 27 | | 14 | Lu Wushuang | 17 | F | 3 | NULL | 8 | Xiaoyao Pai | 15 | | 15 | Duan Yu | 19 | M | 4 | NULL | 1 | Shaolin Pai | 10 | | 15 | Duan Yu | 19 | M | 4 | NULL | 2 | Emei Pai | 7 | | 15 | Duan Yu | 19 | M | 4 | NULL | 3 | QingCheng Pai | 11 | | 15 | Duan Yu | 19 | M | 4 | NULL | 4 | Wudang Pai | 12 | | 15 | Duan Yu | 19 | M | 4 | NULL | 5 | Riyue Shenjiao | 31 | | 15 | Duan Yu | 19 | M | 4 | NULL | 6 | Lianshan Pai | 27 | | 15 | Duan Yu | 19 | M | 4 | NULL | 7 | Ming Jiao | 27 | | 15 | Duan Yu | 19 | M | 4 | NULL | 8 | Xiaoyao Pai | 15 | | 16 | Xu Zhu | 21 | M | 1 | NULL | 1 | Shaolin Pai | 10 | | 16 | Xu Zhu | 21 | M | 1 | NULL | 2 | Emei Pai | 7 | | 16 | Xu Zhu | 21 | M | 1 | NULL | 3 | QingCheng Pai | 11 | | 16 | Xu Zhu | 21 | M | 1 | NULL | 4 | Wudang Pai | 12 | | 16 | Xu Zhu | 21 | M | 1 | NULL | 5 | Riyue Shenjiao | 31 | | 16 | Xu Zhu | 21 | M | 1 | NULL | 6 | Lianshan Pai | 27 | | 16 | Xu Zhu | 21 | M | 1 | NULL | 7 | Ming Jiao | 27 | | 16 | Xu Zhu | 21 | M | 1 | NULL | 8 | Xiaoyao Pai | 15 | | 17 | Lin Chong | 25 | M | 4 | NULL | 1 | Shaolin Pai | 10 | | 17 | Lin Chong | 25 | M | 4 | NULL | 2 | Emei Pai | 7 | | 17 | Lin Chong | 25 | M | 4 | NULL | 3 | QingCheng Pai | 11 | | 17 | Lin Chong | 25 | M | 4 | NULL | 4 | Wudang Pai | 12 | | 17 | Lin Chong | 25 | M | 4 | NULL | 5 | Riyue Shenjiao | 31 | | 17 | Lin Chong | 25 | M | 4 | NULL | 6 | Lianshan Pai | 27 | | 17 | Lin Chong | 25 | M | 4 | NULL | 7 | Ming Jiao | 27 | | 17 | Lin Chong | 25 | M | 4 | NULL | 8 | Xiaoyao Pai | 15 | | 18 | Hua Rong | 23 | M | 7 | NULL | 1 | Shaolin Pai | 10 | | 18 | Hua Rong | 23 | M | 7 | NULL | 2 | Emei Pai | 7 | | 18 | Hua Rong | 23 | M | 7 | NULL | 3 | QingCheng Pai | 11 | | 18 | Hua Rong | 23 | M | 7 | NULL | 4 | Wudang Pai | 12 | | 18 | Hua Rong | 23 | M | 7 | NULL | 5 | Riyue Shenjiao | 31 | | 18 | Hua Rong | 23 | M | 7 | NULL | 6 | Lianshan Pai | 27 | | 18 | Hua Rong | 23 | M | 7 | NULL | 7 | Ming Jiao | 27 | | 18 | Hua Rong | 23 | M | 7 | NULL | 8 | Xiaoyao Pai | 15 | | 19 | Xue Baochai | 18 | F | 6 | NULL | 1 | Shaolin Pai | 10 | | 19 | Xue Baochai | 18 | F | 6 | NULL | 2 | Emei Pai | 7 | | 19 | Xue Baochai | 18 | F | 6 | NULL | 3 | QingCheng Pai | 11 | | 19 | Xue Baochai | 18 | F | 6 | NULL | 4 | Wudang Pai | 12 | | 19 | Xue Baochai | 18 | F | 6 | NULL | 5 | Riyue Shenjiao | 31 | | 19 | Xue Baochai | 18 | F | 6 | NULL | 6 | Lianshan Pai | 27 | | 19 | Xue Baochai | 18 | F | 6 | NULL | 7 | Ming Jiao | 27 | | 19 | Xue Baochai | 18 | F | 6 | NULL | 8 | Xiaoyao Pai | 15 | | 20 | Diao Chan | 19 | F | 7 | NULL | 1 | Shaolin Pai | 10 | | 20 | Diao Chan | 19 | F | 7 | NULL | 2 | Emei Pai | 7 | | 20 | Diao Chan | 19 | F | 7 | NULL | 3 | QingCheng Pai | 11 | | 20 | Diao Chan | 19 | F | 7 | NULL | 4 | Wudang Pai | 12 | | 20 | Diao Chan | 19 | F | 7 | NULL | 5 | Riyue Shenjiao | 31 | | 20 | Diao Chan | 19 | F | 7 | NULL | 6 | Lianshan Pai | 27 | | 20 | Diao Chan | 19 | F | 7 | NULL | 7 | Ming Jiao | 27 | | 20 | Diao Chan | 19 | F | 7 | NULL | 8 | Xiaoyao Pai | 15 | | 21 | Huang Yueying | 22 | F | 6 | NULL | 1 | Shaolin Pai | 10 | | 21 | Huang Yueying | 22 | F | 6 | NULL | 2 | Emei Pai | 7 | | 21 | Huang Yueying | 22 | F | 6 | NULL | 3 | QingCheng Pai | 11 | | 21 | Huang Yueying | 22 | F | 6 | NULL | 4 | Wudang Pai | 12 | | 21 | Huang Yueying | 22 | F | 6 | NULL | 5 | Riyue Shenjiao | 31 | | 21 | Huang Yueying | 22 | F | 6 | NULL | 6 | Lianshan Pai | 27 | | 21 | Huang Yueying | 22 | F | 6 | NULL | 7 | Ming Jiao | 27 | | 21 | Huang Yueying | 22 | F | 6 | NULL | 8 | Xiaoyao Pai | 15 | | 22 | Xiao Qiao | 20 | F | 1 | NULL | 1 | Shaolin Pai | 10 | | 22 | Xiao Qiao | 20 | F | 1 | NULL | 2 | Emei Pai | 7 | | 22 | Xiao Qiao | 20 | F | 1 | NULL | 3 | QingCheng Pai | 11 | | 22 | Xiao Qiao | 20 | F | 1 | NULL | 4 | Wudang Pai | 12 | | 22 | Xiao Qiao | 20 | F | 1 | NULL | 5 | Riyue Shenjiao | 31 | | 22 | Xiao Qiao | 20 | F | 1 | NULL | 6 | Lianshan Pai | 27 | | 22 | Xiao Qiao | 20 | F | 1 | NULL | 7 | Ming Jiao | 27 | | 22 | Xiao Qiao | 20 | F | 1 | NULL | 8 | Xiaoyao Pai | 15 | | 23 | Ma Chao | 23 | M | 4 | NULL | 1 | Shaolin Pai | 10 | | 23 | Ma Chao | 23 | M | 4 | NULL | 2 | Emei Pai | 7 | | 23 | Ma Chao | 23 | M | 4 | NULL | 3 | QingCheng Pai | 11 | | 23 | Ma Chao | 23 | M | 4 | NULL | 4 | Wudang Pai | 12 | | 23 | Ma Chao | 23 | M | 4 | NULL | 5 | Riyue Shenjiao | 31 | | 23 | Ma Chao | 23 | M | 4 | NULL | 6 | Lianshan Pai | 27 | | 23 | Ma Chao | 23 | M | 4 | NULL | 7 | Ming Jiao | 27 | | 23 | Ma Chao | 23 | M | 4 | NULL | 8 | Xiaoyao Pai | 15 | | 24 | Xu Xian | 27 | M | NULL | NULL | 1 | Shaolin Pai | 10 | | 24 | Xu Xian | 27 | M | NULL | NULL | 2 | Emei Pai | 7 | | 24 | Xu Xian | 27 | M | NULL | NULL | 3 | QingCheng Pai | 11 | | 24 | Xu Xian | 27 | M | NULL | NULL | 4 | Wudang Pai | 12 | | 24 | Xu Xian | 27 | M | NULL | NULL | 5 | Riyue Shenjiao | 31 | | 24 | Xu Xian | 27 | M | NULL | NULL | 6 | Lianshan Pai | 27 | | 24 | Xu Xian | 27 | M | NULL | NULL | 7 | Ming Jiao | 27 | | 24 | Xu Xian | 27 | M | NULL | NULL | 8 | Xiaoyao Pai | 15 | | 25 | Sun Dasheng | 100 | M | NULL | NULL | 1 | Shaolin Pai | 10 | | 25 | Sun Dasheng | 100 | M | NULL | NULL | 2 | Emei Pai | 7 | | 25 | Sun Dasheng | 100 | M | NULL | NULL | 3 | QingCheng Pai | 11 | | 25 | Sun Dasheng | 100 | M | NULL | NULL | 4 | Wudang Pai | 12 | | 25 | Sun Dasheng | 100 | M | NULL | NULL | 5 | Riyue Shenjiao | 31 | | 25 | Sun Dasheng | 100 | M | NULL | NULL | 6 | Lianshan Pai | 27 | | 25 | Sun Dasheng | 100 | M | NULL | NULL | 7 | Ming Jiao | 27 | | 25 | Sun Dasheng | 100 | M | NULL | NULL | 8 | Xiaoyao Pai | 15 | +-------+---------------+-----+--------+---------+-----------+---------+----------------+----------+ 200 rows in set (0.00 sec)自然连接(内联接)： 等值联接：把两张表中的对应字段做等值关联 SELECT * FROM students,classes WHERE students.ClassID =classes.CLassID
mysql> SELECT * FROM students,classes WHERE students.CLASSID = classes.CLASSID; +-------+---------------+-----+--------+---------+-----------+---------+----------------+----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | ClassID | Class | NumOfStu | +-------+---------------+-----+--------+---------+-----------+---------+----------------+----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | 2 | Emei Pai | 7 | | 2 | Shi Potian | 22 | M | 1 | 7 | 1 | Shaolin Pai | 10 | | 3 | Xie Yanke | 53 | M | 2 | 16 | 2 | Emei Pai | 7 | | 4 | Ding Dian | 32 | M | 4 | 4 | 4 | Wudang Pai | 12 | | 5 | Yu Yutong | 26 | M | 3 | 1 | 3 | QingCheng Pai | 11 | | 6 | Shi Qing | 46 | M | 5 | NULL | 5 | Riyue Shenjiao | 31 | | 7 | Xi Ren | 19 | F | 3 | NULL | 3 | QingCheng Pai | 11 | | 8 | Lin Daiyu | 17 | F | 7 | NULL | 7 | Ming Jiao | 27 | | 9 | Ren Yingying | 20 | F | 6 | NULL | 6 | Lianshan Pai | 27 | | 10 | Yue Lingshan | 19 | F | 3 | NULL | 3 | QingCheng Pai | 11 | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | 6 | Lianshan Pai | 27 | | 12 | Wen Qingqing | 19 | F | 1 | NULL | 1 | Shaolin Pai | 10 | | 13 | Tian Boguang | 33 | M | 2 | NULL | 2 | Emei Pai | 7 | | 14 | Lu Wushuang | 17 | F | 3 | NULL | 3 | QingCheng Pai | 11 | | 15 | Duan Yu | 19 | M | 4 | NULL | 4 | Wudang Pai | 12 | | 16 | Xu Zhu | 21 | M | 1 | NULL | 1 | Shaolin Pai | 10 | | 17 | Lin Chong | 25 | M | 4 | NULL | 4 | Wudang Pai | 12 | | 18 | Hua Rong | 23 | M | 7 | NULL | 7 | Ming Jiao | 27 | | 19 | Xue Baochai | 18 | F | 6 | NULL | 6 | Lianshan Pai | 27 | | 20 | Diao Chan | 19 | F | 7 | NULL | 7 | Ming Jiao | 27 | | 21 | Huang Yueying | 22 | F | 6 | NULL | 6 | Lianshan Pai | 27 | | 22 | Xiao Qiao | 20 | F | 1 | NULL | 1 | Shaolin Pai | 10 | | 23 | Ma Chao | 23 | M | 4 | NULL | 4 | Wudang Pai | 12 | +-------+---------------+-----+--------+---------+-----------+---------+----------------+----------+ 23 rows in set (0.04 sec) mysql> SELECT students.Name,classes.Class FROM students,classes WHERE students.CLASSID = classes.CLASSID; +---------------+----------------+ | Name | Class | +---------------+----------------+ | Shi Zhongyu | Emei Pai | | Shi Potian | Shaolin Pai | | Xie Yanke | Emei Pai | | Ding Dian | Wudang Pai | | Yu Yutong | QingCheng Pai | | Shi Qing | Riyue Shenjiao | | Xi Ren | QingCheng Pai | | Lin Daiyu | Ming Jiao | | Ren Yingying | Lianshan Pai | | Yue Lingshan | QingCheng Pai | | Yuan Chengzhi | Lianshan Pai | | Wen Qingqing | Shaolin Pai | | Tian Boguang | Emei Pai | | Lu Wushuang | QingCheng Pai | | Duan Yu | Wudang Pai | | Xu Zhu | Shaolin Pai | | Lin Chong | Wudang Pai | | Hua Rong | Ming Jiao | | Xue Baochai | Lianshan Pai | | Diao Chan | Ming Jiao | | Huang Yueying | Lianshan Pai | | Xiao Qiao | Shaolin Pai | | Ma Chao | Wudang Pai | +---------------+----------------+ 23 rows in set (0.00 sec)SELECT * FROM students.name,classes.class WHERE students.ClassID =classes.CLassID（若两张表中的字段名称一样，则指明字段）
别名： 表别名 SELECT students.name,classes.class FROM students AS s,classes AS c WHEREs.CLASSID = c.CLASSID
mysql> SELECT s.Name,c.Class FROM students AS s,classes AS c WHERE s.ClassID = c.ClassID; +---------------+----------------+ | Name | Class | +---------------+----------------+ | Shi Zhongyu | Emei Pai | | Shi Potian | Shaolin Pai | | Xie Yanke | Emei Pai | | Ding Dian | Wudang Pai | | Yu Yutong | QingCheng Pai | | Shi Qing | Riyue Shenjiao | | Xi Ren | QingCheng Pai | | Lin Daiyu | Ming Jiao | | Ren Yingying | Lianshan Pai | | Yue Lingshan | QingCheng Pai | | Yuan Chengzhi | Lianshan Pai | | Wen Qingqing | Shaolin Pai | | Tian Boguang | Emei Pai | | Lu Wushuang | QingCheng Pai | | Duan Yu | Wudang Pai | | Xu Zhu | Shaolin Pai | | Lin Chong | Wudang Pai | | Hua Rong | Ming Jiao | | Xue Baochai | Lianshan Pai | | Diao Chan | Ming Jiao | | Huang Yueying | Lianshan Pai | | Xiao Qiao | Shaolin Pai | | Ma Chao | Wudang Pai | +---------------+----------------+ 23 rows in set (0.00 sec)字段别名 SELECT NAME AS STUNAME FROM students;
mysql> SELECT Name FROM students; +---------------+ | Name | +---------------+ | Shi Zhongyu | | Shi Potian | | Xie Yanke | | Ding Dian | | Yu Yutong | | Shi Qing | | Xi Ren | | Lin Daiyu | | Ren Yingying | | Yue Lingshan | | Yuan Chengzhi | | Wen Qingqing | | Tian Boguang | | Lu Wushuang | | Duan Yu | | Xu Zhu | | Lin Chong | | Hua Rong | | Xue Baochai | | Diao Chan | | Huang Yueying | | Xiao Qiao | | Ma Chao | | Xu Xian | | Sun Dasheng | +---------------+ 25 rows in set (0.00 sec) mysql> SELECT Name As STUName FROM students; +---------------+ | STUName | +---------------+ | Shi Zhongyu | | Shi Potian | | Xie Yanke | | Ding Dian | | Yu Yutong | | Shi Qing | | Xi Ren | | Lin Daiyu | | Ren Yingying | | Yue Lingshan | | Yuan Chengzhi | | Wen Qingqing | | Tian Boguang | | Lu Wushuang | | Duan Yu | | Xu Zhu | | Lin Chong | | Hua Rong | | Xue Baochai | | Diao Chan | | Huang Yueying | | Xiao Qiao | | Ma Chao | | Xu Xian | | Sun Dasheng | +---------------+ 25 rows in set (0.00 sec)条件联接（很少使用）外联结：左外联结：只保留出现在左外连接运算之前（左边）的关系中的元组；left_tb LEFT JOIN right_tb ON 连接条件
mysql> SELECT s.Name,c.Class FROM students AS s LEFT JOIN classes AS c ON s.ClassID = c.ClassID; +---------------+----------------+ | Name | Class | +---------------+----------------+ | Shi Zhongyu | Emei Pai | | Shi Potian | Shaolin Pai | | Xie Yanke | Emei Pai | | Ding Dian | Wudang Pai | | Yu Yutong | QingCheng Pai | | Shi Qing | Riyue Shenjiao | | Xi Ren | QingCheng Pai | | Lin Daiyu | Ming Jiao | | Ren Yingying | Lianshan Pai | | Yue Lingshan | QingCheng Pai | | Yuan Chengzhi | Lianshan Pai | | Wen Qingqing | Shaolin Pai | | Tian Boguang | Emei Pai | | Lu Wushuang | QingCheng Pai | | Duan Yu | Wudang Pai | | Xu Zhu | Shaolin Pai | | Lin Chong | Wudang Pai | | Hua Rong | Ming Jiao | | Xue Baochai | Lianshan Pai | | Diao Chan | Ming Jiao | | Huang Yueying | Lianshan Pai | | Xiao Qiao | Shaolin Pai | | Ma Chao | Wudang Pai | | Xu Xian | NULL | | Sun Dasheng | NULL | +---------------+----------------+ 25 rows in set (0.00 sec)右外联结：只保留出现在右外连接运算之后（右边）的关系中的元组；left_tb RIGHT JOIN right_tb ON 连接条件
mysql> SELECT * FROM students; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+ 25 rows in set (0.06 sec) mysql> SELECT * FROM classes; +---------+----------------+----------+ | ClassID | Class | NumOfStu | +---------+----------------+----------+ | 1 | Shaolin Pai | 10 | | 2 | Emei Pai | 7 | | 3 | QingCheng Pai | 11 | | 4 | Wudang Pai | 12 | | 5 | Riyue Shenjiao | 31 | | 6 | Lianshan Pai | 27 | | 7 | Ming Jiao | 27 | | 8 | Xiaoyao Pai | 15 | +---------+----------------+----------+ 8 rows in set (0.02 sec) mysql> SELECT s.Name,c.Class FROM students AS s RIGHT JOIN classes AS c ON s.ClassID = c.ClassID; +---------------+----------------+ | Name | Class | +---------------+----------------+ | Shi Potian | Shaolin Pai | | Wen Qingqing | Shaolin Pai | | Xu Zhu | Shaolin Pai | | Xiao Qiao | Shaolin Pai | | Shi Zhongyu | Emei Pai | | Xie Yanke | Emei Pai | | Tian Boguang | Emei Pai | | Yu Yutong | QingCheng Pai | | Xi Ren | QingCheng Pai | | Yue Lingshan | QingCheng Pai | | Lu Wushuang | QingCheng Pai | | Ding Dian | Wudang Pai | | Duan Yu | Wudang Pai | | Lin Chong | Wudang Pai | | Ma Chao | Wudang Pai | | Shi Qing | Riyue Shenjiao | | Ren Yingying | Lianshan Pai | | Yuan Chengzhi | Lianshan Pai | | Xue Baochai | Lianshan Pai | | Huang Yueying | Lianshan Pai | | Lin Daiyu | Ming Jiao | | Hua Rong | Ming Jiao | | Diao Chan | Ming Jiao | | NULL | Xiaoyao Pai | +---------------+----------------+ 24 rows in set (0.00 sec)全外联结（mysql不支持）：二者左右都出现练习：导入hellodb.sql，完成以下题目：1、显示前5位同学的姓名、课程及成绩；2、显示其成绩高于80的同学的名称及课程；3、求前8位同学每位同学自己两门课的平均成绩，并按降序排列；4、显示每门课程课程名称及学习了这门课的同学的个数；1、
mysql> SELECT * FROM students; +-------+---------------+-----+--------+---------+-----------+ | StuID | Name | Age | Gender | ClassID | TeacherID | +-------+---------------+-----+--------+---------+-----------+ | 1 | Shi Zhongyu | 22 | M | 2 | 3 | | 2 | Shi Potian | 22 | M | 1 | 7 | | 3 | Xie Yanke | 53 | M | 2 | 16 | | 4 | Ding Dian | 32 | M | 4 | 4 | | 5 | Yu Yutong | 26 | M | 3 | 1 | | 6 | Shi Qing | 46 | M | 5 | NULL | | 7 | Xi Ren | 19 | F | 3 | NULL | | 8 | Lin Daiyu | 17 | F | 7 | NULL | | 9 | Ren Yingying | 20 | F | 6 | NULL | | 10 | Yue Lingshan | 19 | F | 3 | NULL | | 11 | Yuan Chengzhi | 23 | M | 6 | NULL | | 12 | Wen Qingqing | 19 | F | 1 | NULL | | 13 | Tian Boguang | 33 | M | 2 | NULL | | 14 | Lu Wushuang | 17 | F | 3 | NULL | | 15 | Duan Yu | 19 | M | 4 | NULL | | 16 | Xu Zhu | 21 | M | 1 | NULL | | 17 | Lin Chong | 25 | M | 4 | NULL | | 18 | Hua Rong | 23 | M | 7 | NULL | | 19 | Xue Baochai | 18 | F | 6 | NULL | | 20 | Diao Chan | 19 | F | 7 | NULL | | 21 | Huang Yueying | 22 | F | 6 | NULL | | 22 | Xiao Qiao | 20 | F | 1 | NULL | | 23 | Ma Chao | 23 | M | 4 | NULL | | 24 | Xu Xian | 27 | M | NULL | NULL | | 25 | Sun Dasheng | 100 | M | NULL | NULL | +-------+---------------+-----+--------+---------+-----------+ 25 rows in set (0.00 sec) mysql> SELECT * FROM courses; +----------+----------------+ | CourseID | Course | +----------+----------------+ | 1 | Hamo Gong | | 2 | Kuihua Baodian | | 3 | Jinshe Jianfa | | 4 | Taiji Quan | | 5 | Daiyu Zanghua | | 6 | Weituo Zhang | | 7 | Dagou Bangfa | +----------+----------------+ 7 rows in set (0.05 sec) mysql> SELECT * FROM coc; +----+---------+----------+ | ID | ClassID | CourseID | +----+---------+----------+ | 1 | 1 | 2 | | 2 | 1 | 5 | | 3 | 2 | 2 | | 4 | 2 | 6 | | 5 | 3 | 1 | | 6 | 3 | 7 | | 7 | 4 | 5 | | 8 | 4 | 2 | | 9 | 5 | 1 | | 10 | 5 | 9 | | 11 | 6 | 3 | | 12 | 6 | 4 | | 13 | 7 | 4 | | 14 | 7 | 3 | +----+---------+----------+ 14 rows in set (0.10 sec) mysql> SELECT * FROM scores; +----+-------+----------+-------+ | ID | StuID | CourseID | Score | +----+-------+----------+-------+ | 1 | 1 | 2 | 77 | | 2 | 1 | 6 | 93 | | 3 | 2 | 2 | 47 | | 4 | 2 | 5 | 97 | | 5 | 3 | 2 | 88 | | 6 | 3 | 6 | 75 | | 7 | 4 | 5 | 71 | | 8 | 4 | 2 | 89 | | 9 | 5 | 1 | 39 | | 10 | 5 | 7 | 63 | | 11 | 6 | 1 | 96 | | 12 | 7 | 1 | 86 | | 13 | 7 | 7 | 83 | | 14 | 8 | 4 | 57 | | 15 | 8 | 3 | 93 | +----+-------+----------+-------+ 15 rows in set (0.05 sec) mysql> SELECT Name,Course,Score FROM students AS s,courses AS c,coc,scores AS ss WHERE s.ClassID = coc.ClassID && coc.CourseID = c.CourseID && s.StuID <= 5 && s.StuID = ss.StuID && coc.CourseID = ss.CourseID; +-------------+----------------+-------+ | Name | Course | Score | +-------------+----------------+-------+ | Shi Zhongyu | Kuihua Baodian | 77 | | Shi Zhongyu | Weituo Zhang | 93 | | Shi Potian | Kuihua Baodian | 47 | | Shi Potian | Daiyu Zanghua | 97 | | Xie Yanke | Kuihua Baodian | 88 | | Xie Yanke | Weituo Zhang | 75 | | Ding Dian | Daiyu Zanghua | 71 | | Ding Dian | Kuihua Baodian | 89 | | Yu Yutong | Hamo Gong | 39 | | Yu Yutong | Dagou Bangfa | 63 | +-------------+----------------+-------+ 10 rows in set (0.03 sec) 2/3 mysql> SELECT Name,AVG(Score) FROM students AS s,courses AS c,coc,scores AS ss WHERE s.ClassID = coc.ClassID && coc.CourseID = c.CourseID && s.StuID <= 8 && s.StuID = ss.StuID && coc.CourseID = ss.CourseID GROUP BY Name ORDER BY AVG(Score) DESC; +-------------+------------+ | Name | AVG(Score) | +-------------+------------+ | Shi Qing | 96.0000 | | Shi Zhongyu | 85.0000 | | Xi Ren | 84.5000 | | Xie Yanke | 81.5000 | | Ding Dian | 80.0000 | | Lin Daiyu | 75.0000 | | Shi Potian | 72.0000 | | Yu Yutong | 51.0000 | +-------------+------------+ 8 rows in set (0.01 sec)
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