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primary and foreign key?? (1 Viewer)
- Thread starter rach_1
- Start date
Lwaxana
Betazed Ambassador
Keys are fields that are used to sort and retrieve information.
Primary key is a field in which the data is unique
eg in Student Field - primary key would be StudentId
Foreign key is a field that is a Primary Key in another table
eg in Classes table which has ClassId as primary key
TeacherId could be foreign key
does that answer yr query ?
Primary key is a field in which the data is unique
eg in Student Field - primary key would be StudentId
Foreign key is a field that is a Primary Key in another table
eg in Classes table which has ClassId as primary key
TeacherId could be foreign key
does that answer yr query ?
Kd14
Member
- Joined
- Oct 17, 2004
- Messages
- 87
- Gender
- Male
- HSC
- 2010
The way I remember it is that a Primary key is unique. Like an ID no.
Foreign key is a primary key that's in a field that already has its own primary key.
EG.
Family has a primary key Family ID.
Student has a primary key StudentID plus a foreign key Family ID.
Foreign key is a primary key that's in a field that already has its own primary key.
EG.
Family has a primary key Family ID.
Student has a primary key StudentID plus a foreign key Family ID.
Last edited:
to use Kd14's example:
Table:Family has the primary field FAMILY_ID. Each FAMILY_ID in the Family table MUST be unique.
Table:Student has the primary field STUDENT_ID, which must be unique, and the FOREIGN_KEY FAMILY_ID from the family table. This foreign key can exist MORE THAN ONE TIME in the Students table, but exists only once in the Family table.
... this would be an example of a Many(students)-to-one(family) relationship!
Wordy I know, but i hope this makes it a bit clearer.
Table:Family has the primary field FAMILY_ID. Each FAMILY_ID in the Family table MUST be unique.
Table:Student has the primary field STUDENT_ID, which must be unique, and the FOREIGN_KEY FAMILY_ID from the family table. This foreign key can exist MORE THAN ONE TIME in the Students table, but exists only once in the Family table.
... this would be an example of a Many(students)-to-one(family) relationship!
Wordy I know, but i hope this makes it a bit clearer.
^caTaHolic^
New Member
can sum1 help me too?
im doing an assessment and we have to create a database for a music store, selling instruments, cds, dvs etc..can u help me and tell me wot tables i would need to create and the relationship between them, i relli duno wot to do and its due in a wk!! thx
im doing an assessment and we have to create a database for a music store, selling instruments, cds, dvs etc..can u help me and tell me wot tables i would need to create and the relationship between them, i relli duno wot to do and its due in a wk!! thx
seremify007
Junior Member
Haha ummm... It's hard to say =P But you could have like a table for inventory and a table for products... like, instead of saying (in the Inventory table) that you have 100 Green flutes, you could make it ItemNo. 1, Quantity 100, and then in the Products table, say that ItemNo. 1 is a Green flute. After this you could create an orders table, a customer table, etc..
Just remember- primary key is something which has to be unique. Whenever I need one, I just make the "ID" field (or I create an ID field) and make that the primary key. Foreign key is the primary key from another table.
Just remember- primary key is something which has to be unique. Whenever I need one, I just make the "ID" field (or I create an ID field) and make that the primary key. Foreign key is the primary key from another table.