数据库SQL学习的经典案例：学生专业老师分数表的操练

mysql> desc SC;
+-------+---------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------------+------+-----+---------+-------+
| S_id | varchar(10) | YES | | NULL | |
| C_id | varchar(10) | YES | | NULL | |
| score | decimal(18,1) | YES | | NULL | |
+-------+---------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

mysql> select * from SC;
+------+------+-------+
| S_id | C_id | score |
+------+------+-------+
| 01 | 01 | 80.0 |
| 01 | 02 | 90.0 |
| 01 | 03 | 99.0 |
| 02 | 01 | 70.0 |
| 02 | 02 | 60.0 |
| 02 | 03 | 80.0 |
| 03 | 01 | 80.0 |
| 03 | 02 | 80.0 |
| 03 | 03 | 80.0 |
| 04 | 01 | 50.0 |
| 04 | 02 | 30.0 |
| 04 | 03 | 20.0 |
| 05 | 01 | 76.0 |
| 05 | 02 | 87.0 |
| 06 | 01 | 31.0 |
| 06 | 03 | 34.0 |
| 07 | 02 | 89.0 |
| 07 | 03 | 98.0 |
| 08 | 04 | 79.0 |
| 11 | 03 | 77.9 |
| 12 | 02 | 47.9 |
| 12 | 04 | 47.9 |
| 11 | 01 | 77.9 |
| 01 | 04 | 73.9 |
| 01 | 05 | 83.9 |
| 06 | 04 | 75.0 |
| 06 | 05 | 85.0 |
| 11 | 05 | 81.0 |
| 11 | 04 | 91.0 |
+------+------+-------+
29 rows in set (0.00 sec)


--1
select B.* from SC B where B.C_id = '01' 
and not exists(select * from SC B2 where B.S_id = B2.S_id and B2.C_id = '02');

--2
select * from 
(select B.S_id, B.C_id aC_id, B.score ascore, B2.C_id bC_id, B2.score bscore 
from SC B inner join SC B2 
on B.S_id = B2.S_id and B.C_id = '01' and B2.C_id != '01') 
BBB 
where not exists 
(select * from (select B.S_id, B.C_id aC_id, B.score ascore, B2.C_id bC_id, B2.score bscore 
from SC B inner join SC B2 
on B.S_id = B2.S_id and B.C_id = '01' and B2.C_id != '01') 
CCC where BBB.S_id = CCC.S_id and CCC.bC_id = '02' );

--3
select * from SC where C_id = '01' 
and S_id not in 
(select distinct S_id from SC where C_id = '02');

--4
select B.S_id, B.C_id aC_id, B.score ascore, B2.C_id bC_id, B2.score bscore 
from SC B inner join SC B2 
on B.S_id = B2.S_id and B.C_id = '01' and B2.C_id != '01' 
group by S_id having (aC_id, bC_id) != ('01','02');

--5
select B.*, B2.* from SC B left join SC B2 
on B.S_id = B2.S_id and B2.C_id = '02' 
where B.C_id = '01' and B2.C_id is null;

--6
select B.*, B2.* from SC B right join SC B2 
on B.S_id = B2.S_id and B.C_id = '02' 
where B2.C_id = '01' and B.C_id is null;

--7
select B.S_id, B.C_id aC_id, B.score ascore, B2.C_id bC_id, B2.score bscore 
from SC B inner join SC B2 
on B.S_id = B2.S_id and B.C_id = '01' 
and B2.C_id != '01' 
group by S_id having nullif(bC_id, '02') >> 1;