Question

I have two SQL tables Student and Class.

In Student table, the fields are studentNo, studentName, classNo

In Class table, fields are classNo, className, teacherName

what I am trying to do is construct a query to list all students who are in the history class.

Here is my query:

SELECT studentName
FROM Student s, Class c
WHERE s.classNo = c.classNo AND
   c.className = ‘history’;

But I am not 100% sure about the above query. and I am thinking maybe the following one can work than the above one:

SELECT studentName
FROM Student s, Class c
WHERE c.className = ‘history’ AND
   s.classNo = c.classNo;

Can anyone help me find the correct query to this problem? thank you

Answer 1

Your current query seems fine but mind if you convert it into ANSI SQL_92 format (more clear, and may not lead to cross join),

SELECT studentName
FROM Student s INNER JOIN Class c
       ON s.classNo = c.classNo
WHERE  c.className = 'history';

There is no difference if you interchange the two. In math, commutative law states that A + B = B + A.