MySQL - 使用左连接获取未分配资源的复杂查询

Question

我有以下 fiddle http://sqlfiddle.com/#!2/5c089/2

这是数据库表的架构:

类:

id
school_id

classes_academic_years:

id
class_id
name
academic_year_id
grade

classes_subjects:

id
class_academic_year_id
subject_id

class_masters:

id
class_academic_year_id
professor_id

教授:

id
school_id
first_name
last_name

professors_subjects:

id
professor_id
subject_id

professors_classes_subjects:

id
professor_id
class_academic_year_id
subject_id

主题:

id
name
school_id
default

我有两个问题:

select subjects.* from subjects
inner join professors_subjects on professors_subjects.subject_id = subjects.id
where professors_subjects.professor_id = 198;

和

SELECT DISTINCT `subjects`.* 
FROM `subjects` 
INNER JOIN `classes_subjects` ON classes_subjects.subject_id = subjects.id 
INNER JOIN `classes_academic_years` ON classes_academic_years.id = classes_subjects.class_academic_year_id 
LEFT JOIN `professors_classes_subjects` ON professors_classes_subjects.class_academic_year_id = classes_subjects.class_academic_year_id and professors_classes_subjects.subject_id = classes_subjects.subject_id 
left join `class_masters` on class_masters.class_academic_year_id = classes_academic_years.id
WHERE ((professors_classes_subjects.id is null or professors_classes_subjects.professor_id = 198) and class_masters.professor_id = 198 ) 
AND (classes_academic_years.academic_year_id = 3) 
AND (subjects.default = 0) 
ORDER BY `name` asc;

第一个只是获取分配给某个教授(professor_id = 198)的所有科目。

第二个将分配给某个教授(professor_id = 198)的所有科目提取到该教授是类主任的类(class)，以及该类(class)的所有未分配给任何其他教授的科目。 (例如，professor_id = 198 已为 class_id = 426 分配了 subject_id = 67，但该类(class)还有两个未分配的科目需要获取)。

在给定的示例中，第一个查询获取 ID 为 76 和 67 的主题，第二个查询获取 ID 为 86、72 和 67 的主题。

这两个查询都工作得很好。但是，我需要结合这两者的第三个查询(例如，它应该获取 ID 为 76、67、86 和 72 的主题)。我更喜欢使用左连接，从而避免使用 UNION 运算符。

你对第三个查询有什么想法吗？

Answer 1

试试这个:

SELECT DISTINCT `subjects`.* 
FROM `subjects` 
INNER JOIN `classes_subjects` ON classes_subjects.subject_id = subjects.id 
INNER JOIN `classes_academic_years` ON classes_academic_years.id = classes_subjects.class_academic_year_id 
LEFT JOIN `professors_classes_subjects` ON professors_classes_subjects.class_academic_year_id = classes_subjects.class_academic_year_id and professors_classes_subjects.subject_id = classes_subjects.subject_id 
left join `class_masters` on class_masters.class_academic_year_id = classes_academic_years.id

left join professors_subjects on professors_subjects.subject_id = subjects.id

WHERE (((professors_classes_subjects.id is null or professors_classes_subjects.professor_id = 198) and class_masters.professor_id = 198 ) 
AND (classes_academic_years.academic_year_id = 3) 
AND (subjects.default = 0)) 

OR professors_subjects.professor_id = 198

ORDER BY `name` asc;

我引入了另一个左连接(连接你在第一个查询中的表)，并在整个 WHERE 子句中添加了 OR 逻辑。