如何限制左连接？

Question

我做了两个表这样

degree_plan        student_record 
------------------------------  ---------------------------- 
major course  course_no  ID  course_no  grade   
------------------------------  ---------------------------- 
COE  COE200  1    4455  1   A 
COE  COE305  2    4455  2   C 
COE  COE400  3    3333  4   B 
SWE  SWE214  4 
SWE  SWE344  5 
SWE  SWE444  6 

course_no是我如何写SQL查询来给我这样where ID=4455 and the major = COE

-------------------------- 
major course  grade 
-------------------------- 
COE  COE200  A 
COE  COE305  C 
COE  COE400  NULL 

Answer 1

再尝试这种方式

select a.mjor, a.course, b.grade 
from degree_plan as a 
left join student_record as b on a.course_no=b.course_no and b.id=4455 
where a.major='COE' 

Answer 2

select * 
from degree_plan 
left join studen`t_record 
on studen`t_record.course_no = degree_plan.course_no 
where major = 'COE' 

表

之间的关系你需要专业在哪里过滤

Answer 3

试试这个：

select a.major, a.course, b.grade 
from degree_plan a 
left join studen`t_record b on b.course_no = a.course_no 
where a.major = 'COE' 

你甚至都不需要像条款，因为主要的领域并不比COE

Answer 4

SELECT degree_plan.major, degree_plan.course, studen't_record.grade 
    FROM degree_plan 
LEFT JOIN Student_record ON degree_plan.course_no=student_record.course_no where degree.major='COE';