如何使用 PostgreSQL 中的变量创建具有内部连接的视图？

Question

我正在使用 PostgreSQL 数据库。我需要创建一个视图，该视图由多个表上的连接查询组成，但我被困在一个点上。请阅读下表定义和我创建的查询。

Tables:

Students
---------
id -> UUID
full_name -> VARCHAR
email_id -> VARCHAR
location -> VARCHAR
created_at -> timestamp
modified_at -> timestamp

Subjects
--------
id -> UUID
title -> VARCHAR
classroom -> VARCHAR
created_at -> TIMESTAMP


Applications
------------
id -> UUID
student_id -> FOREIGN KEY (Students.id)
subject_id -> FOREIGN KEY (Subjects.id)
verified -> BOOLEAN
application_response -> JSON
status_id -> FOREIGN KEY (ApplicationStatus.id)
created_at -> TIMESTAMP

ApplicationStatus
-----------------
id -> UUID
application_status -> VARCHAR
category -> VARCHAR

Scores
-------
student_id -> FOREIGN KEY (Students.id)
subject_id -> FOREIGN KEY (Subjects.id)
score -> NUMERIC

以下是我创建的 SQL 查询：

create or replace view testing_list_view as 
select c.id as student_id,
a.subject_id as subject_uid,
c.full_name, 
c.email_id,  
c.created_at, 
p.score, 
s.application_status,
a.verified,
a.application_response
from students c
inner join scores p
on p.student_id=c.id and p.subject_id = 'ff342ada-f5gb-44fb-bdth-44e3n59f5448'
inner join applications a
on a.student_id = c.id and a.subject_id= 'ff342ada-f5gb-44fb-bdth-44e3n59f5448'
inner join applicationstatus s 
on s.id = a.status_id
where c.id in 
(select student_id from applications where subject_id='ff342ada-f5gb-44fb-bdth-44e3n59f5448')

在这里，我正在获取给定subject_id 的学生列表，以及我需要加入的分数、application_status 和其他一些字段。

我的要求是为此查询创建一个视图，以便仅将 subject_id 传递给视图 (select * from testing_list_view where subject_uid='ff342ada-f5gb-44fb-bdth-44e3n59f5448')，然后我将获得已申请给定主题的学生列表。但是，我被困在这里，就像在上面的连接查询中一样，subject_id 在连接子句中多次需要并且是硬编码的。所以，我无法让它成为一个视图。

我在想是否存在某种变量，在 join 子句中，我将在必需的子句中使用该变量，并在查询视图时将值 (subject_id) 传递给它。

如果需要进一步说明，请告诉我。

Answer 1

您应该定义视图没有WHERE 子句和subject_id 的所有其他限制：

create or replace view testing_list_view as 
select c.id as student_id,
       a.subject_id as subject_uid,
       c.full_name, 
       c.email_id,  
       c.created_at, 
       p.score, 
       s.application_status,
       a.verified,
       a.application_response
from students c
   inner join scores p
      on p.student_id=c.id
   inner join applications a
      on a.student_id = c.id and a.subject_id = p.subject_id
   inner join applicationstatus s 
      on s.id = a.status_id;

您在使用视图时指定条件，例如

SELECT * FROM testing_list_view
WHERE subject_uid = 'ff342ada-f5gb-44fb-bdth-44e3n59f5448';