How to have multiple condition on one column

All we need is an easy explanation of the problem, so here it is.

I have table with students – name, id

and table with grades – id, grade value, discipline.

Each students has few grades. I want to select only the students with grade = 2 and grade = 6 in the same time.

SELECT NAME

FROM STUDENTS, GRADES 

WHERE STUDENTDS.ID = GRADES.ID 

AND GRADE = 2 AND GRADE = 6

The logical condition can’t be valid there. Which is the function that I need?

How to solve :

I know you bored from this bug, So we are here to help you! Take a deep breath and look at the explanation of your problem. We have many solutions to this problem, But we recommend you to use the first method because it is tested & true method that will 100% work for you.

Method 1

SELECT NAME 
FROM STUDENTS s
WHERE EXISTS (SELECT 1 FROM GRADES WHERE ID = s.ID AND GRADE = 2)
    AND EXISTS (SELECT 1 FROM GRADES WHERE ID = s.ID AND GRADE = 6) 

or if you don’t have multiple records for some grades for particular users:

SELECT NAME
FROM STUDENTS
JOIN GRADES ON STUDENTS.ID = GRADES.ID
WHERE GRADE = 2 OR GRADE = 6
GROUP BY ID, NAME
HAVING COUNT(1) = 2

Note: Use and implement method 1 because this method fully tested our system.
Thank you 🙂

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