Database design for user packages and credit system

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SQL

MySQL

database

I am working on web application in which user can purchase packages. On the base of these packages user can do different operations. Currently I am using following structure.

Table - Packages

PackageId (PK)	Name	Amount	PackageTypeId
1	Startup	3000	1
2	Premium	5000	1
3	Professional	8000	2

Table - PackageType

PackageTypeId (PK)	Name
1	Deal
2	Business

Table - UserPackages

UserPackageId (PK)	UserId	PackageId (FK)	ExpireDate	isActive
1 (PK)	300	1 (FK)	2013-2-10	yes

Table - UserInvoices

InvoiceId (PK)	UserId	UserPackageId (FK)	Amount	TransactionId
1	300	1	3000	200000333

My Questions Are.

Is this database design is correct
Now i want user can upgrade his package

(Startup --> Premium or Professional)
(Premium --> Professional)

Where these package priority should be saved?

My thought. I have to create new table ( PackagePriority ) with following structure

PriorityId (PK) - PackageId (FK) - PriorPackage (this will also PackageId with different name)

1 (PK) - 1 (FK) - 2 (FK)

2 (PK) - 1 (FK) - 3 (FK)

3 (PK) - 2 (FK) - 3 (FK)

is this right idea?

How can i find user current package is upgradeable to other packages?