Primary Key :- Primary key uniquely identify a record in the table.
Foreign Key :- Foreign key is a field in the table that is primary key in another table.
Table Name: User
Columns:
UserID PK
EmailAddress
Password
Gender
TableName: Friends
Columns:
UserID PK FK
FriendID PK FK
(This table features a composite primary key made up of the two foreign
keys, both pointing back to the user table. One ID will point to the
logged in user, the other ID will point to the individual friend
of that user)
Example Usage:
Table User
—————
UserID EmailAddress Password Gender
—————————————————————
1 satya@thered.black satya@123 M
2 siva@thered.black siva@123 M
3 naveen@thered.black naveen@123 M
Table Friends
——————
UserID FriendID
———————
1 2
1 3
2 3
This will show that satya is friends with both siva and naveen and that siva is also friends with naveen.
Now when showing the friends-list to a particular user, a simple sql would do that:
Select FriendID
From Friends
Where UserID = " where is the id of the logged-in user “
If you want to find siva Friends ?
SELECT FriendID
FROM Friends
WHERE UserID = ‘2’
UNION ALL
SELECT UserID
FROM Friends
WHERE FriendID = ‘2’
Friend List DB Structure for Game
4/
5
Oleh
Unknown