LBD2

--If you know the name of the students who are studying science subject, you can get their id's by using this query below,

SELECT id, first_name
FROM student_details
WHERE first_name IN ('Rahul', 'Stephen');

--but, if you do not know their names, then to get their id's you need to write the query in this manner,

SELECT id, first_name
FROM student_details
WHERE first_name IN (SELECT first_name
FROM student_details
WHERE subject= 'Science');

Subquery Output:
----------------------
| student details    |
|--------------------|
|  id   | first_name |
|-------|------------|
| 100   | Rahul      |
| 102   | Stephen    |
----------------------