When reading about UNIQUE, I understand the concept but when it comes to the practical part of it, I get confused and I'm unsure of what it means.
What I do understand, is that there are two ways to make an attribute UNIQUE, through an index or a unqiue constraint (except Primary key of course). The only difference seems to be that the constraint has the additional "unique key". So here are my questions;
A unique key is created for a constraint but not for a unique index, what’s the point with the key and without?
Can’t drop constraint before dropping index? Why, what’s the point? Is it like this for “additional security”?
What’s the relationship between and UQ key and UQ index? How they are related?
Is it more ”secure” to choose a constraint, if you really want an attribute to stay Unique because you can’t disable a constraint? (Because there is less room for mistakes like disabling the uniqueness of an attribute because you can’t disable a constraint)
I already know that you can use a constraint as an index.
