I've got several tables one is a table of classes (index by ClassID)
Another table is "ClassList" (index by ClassListID) the second column is ClassID how can I search for all students who have the ClassID of 9 for example?

I have this code

SELECT * FROM ClassData WHERE ClassID = 6

It returns nothing in SQL Server even though I can see rows in ClassData with the ClassID of 6.

What is wrong?