SQL 三個表聯接的join寫法

select

university,
difficult_level,
count(qpd.question_id) /
count(distinct qpd.device_id) as
**g_answer_cnt
from question_practice_detail as
qpdleft
join user_profile as
upon up.device_id=
qpd.device_id
left
join question_detail as
qdon qd.question_id=
qpd.question_id
group
by university, difficult_level

資料：統計每個學校各難度的使用者平均刷題數

關鍵字：每個，各，不同，用group by

drop

table
ifexists
`user_profile`;
drop
table
ifexists
`question_practice_detail`;
drop
table
ifexists
`question_detail`;
create
table
`user_profile` (
`id` 
intnot
null
,`device_id` 
intnot
null
,`gender` 
varchar(14) not
null
,`age` 
int,
`university` 
varchar(32) not
null
,`gpa` 
float
,`active_days_within_30` 
int,
`question_cnt` 
int,
`answer_cnt` 
int);
create
table
`question_practice_detail` (
`id` 
intnot
null
,`device_id` 
intnot
null
,`question_id`
intnot
null
,`result` 
varchar(32) not
null
);create
table
`question_detail` (
`id` 
intnot
null
,`question_id`
intnot
null
,`difficult_level` 
varchar(32) not
null
);insert
into user_profile values(1,2138,'
male
',21,'
北京大學
',3.4,7,2,12
);insert
into user_profile values(2,3214,'
male
',null,'
復旦大學
',4.0,15,5,25
);insert
into user_profile values(3,6543,'
female
',20,'
北京大學
',3.2,12,3,30
);insert
into user_profile values(4,2315,'
female
',23,'
浙江大學
',3.6,5,1,2
);insert
into user_profile values(5,5432,'
male
',25,'
山東大學
',3.8,20,15,70
);insert
into user_profile values(6,2131,'
male
',28,'
山東大學
',3.3,15,7,13
);insert
into user_profile values(7,4321,'
male
',28,'
復旦大學
',3.6,9,6,52
);insert
into question_practice_detail values(1,2138,111,'
wrong');
insert
into question_practice_detail values(2,3214,112,'
wrong');
insert
into question_practice_detail values(3,3214,113,'
wrong');
insert
into question_practice_detail values(4,6543,111,'
right');
insert
into question_practice_detail values(5,2315,115,'
right');
insert
into question_practice_detail values(6,2315,116,'
right');
insert
into question_practice_detail values(7,2315,117,'
wrong');
insert
into question_practice_detail values(8,5432,117,'
wrong');
insert
into question_practice_detail values(9,5432,112,'
wrong');
insert
into question_practice_detail values(10,2131,113,'
right');
insert
into question_practice_detail values(11,5432,113,'
wrong');
insert
into question_practice_detail values(12,2315,115,'
right');
insert
into question_practice_detail values(13,2315,116,'
right');
insert
into question_practice_detail values(14,2315,117,'
wrong');
insert
into question_practice_detail values(15,5432,117,'
wrong');
insert
into question_practice_detail values(16,5432,112,'
wrong');
insert
into question_practice_detail values(17,2131,113,'
right');
insert
into question_practice_detail values(18,5432,113,'
wrong');
insert
into question_practice_detail values(19,2315,117,'
wrong');
insert
into question_practice_detail values(20,5432,117,'
wrong');
insert
into question_practice_detail values(21,5432,112,'
wrong');
insert
into question_practice_detail values(22,2131,113,'
right');
insert
into question_practice_detail values(23,5432,113,'
wrong');
insert
into question_detail values(1,111,'
hard');
insert
into question_detail values(2,112,'
medium');
insert
into question_detail values(3,113,'
easy');
insert
into question_detail values(4,115,'
easy');
insert
into question_detail values(5,116,'
medium');
insert
into question_detail values(6,117,'
easy
');

JOIN 在ACESS與SQL的不同寫法

多個left join 不在access 和sql的寫法是不同的 如 access select g.ccbh,g.jyrq,g.10ib老化後 g.033ib老化後 g.05lib老化後 h.05l02ib老化後 from select e.ccbh,e.jyrq,e.10ib老化後 e.033i...

tcp socket修改三個表

insert into mes adapter adapterid,adaptertype,adaptername,adapterstate,createdate,updatedate,techname,endname,description,packagename,srfun,rfun,macfu...

Sql語言 組合兩個表 join

sql中常用的連線方式 組合兩個 兩表中至少存在乙個匹配時，返回匹配項兩表合併的內容。select column name s from table name1 inner join table name2 on table name1.column name table name2.column ...