时间:2021-07-01 10:21:17 帮助过:44人阅读
数据库SQL学习的经典案例:学生专业老师分数表的操练;针对一个问题------选了课程1而没有选课程2的学生有哪些? 下面的SQL语句是各个不同的写法,整理下~ 无 mysql desc SC;+-------+---------------+------+-----+---------+-------+| Field | Type | Null
数据库SQL学习的经典案例:学生专业老师分数表的操练;针对一个问题------选了课程1而没有选课程2的学生有哪些?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;