how can I convert this SQL statement with nested IN clauses to a JOIN format - sql

Question

Here are the very simplified versions of my three tables.
Schools_Subjects Table
SchoolId
SubjectId
1
2
5
1
5
6
The above table contains only parent subject IDs.
Subjects Table
SubjectId
Name
ParentSubjectId
1
Science
{NULL}
2
Mathematics
{NULL}
3
Biology
1
4
Physics
1
5
Chemistry
1
6
History
{NULL}
7
Elementary Math
2
8
Calculus
2
Questions Table
QuestionId
Text
SubjectId
1
What is 2 + 2
7
2
Tell me the fastest animal name
3
3
Salt is composed of which two elements
5
4
How to divide 6 apples among 3 students
7
I want to fetch all the questions given a (or multiple) school ID. For example for schoolId:5, I have the below SQL query:
SELECT *
FROM Questions
WHERE SubjectId IN (
SELECT SubjectId
FROM Subjects
WHERE ParentSubjectId IN (
SELECT SubjectId
FROM Schools_Subjects
WHERE SchoolId = 5
)
)
My above query works but I want to change it into a JOIN format query.
I work on SQL Server, but a ANSI-SQL query will be highly appreciated.

Answer 1

If using Mysql:
SELECT Q.*
FROM Questions Q
JOIN (
SELECT S.SubjectId
FROM Subjects S
JOIN Schools_Subjects SS
ON S.ParentSubjectId = SS.SubjectId AND SS.SchoolId = 5
) t1
ON Q.SubjectID = t1.SubjectId
QuestionId Text SubjectId X
1 2 Tell me the fastest animal name 3 NA
2 3 Salt is composed of which two elements 5 NA
Which is the same results produced by your code