relationships- in databases... (1 Viewer)

[kieransgirl]

can anyone describe the types of relationships to me in laymans terms? one to many, one to one, many to many...

 

[Viper]

Well, let me see if i can put it in laymans terms... (i can do when making a database, but its hard to explain....)

One to One:

If one field can have only one unique value (like in a primary ID), and it can only correspond to another unique value, the relationship must be One-to-One.... You get me?

Eg. "Client_ID" related to "Stock_ID".
There can be only one client allocated to each client ID. The same applies for Stock ID.

One-To-Many:

If One unique value can somehow relate to a value that could be multiple values, the relationship should be One-to-Many.

Eg. "Stock_ID" related to "Order_ID"

There can only be one piece of stock allocated to the stock ID, but there can be many pieces of stock related to one particular order... hmm getting confusing?

Many-To-Many:

If a field that can be one of many values relates to another field that can hold many values, the relationship should be Many-To-Many.

Eg. "Order_ID" related to "Payment_ID"

Many orders can be related to many payments (like if the payments are made in installments...)

Im sorry i couldnt make it clearer... It'd be much easier to explain with a schema..

I hope this helps you

Cheers

 

[jayk]

haha your a legend viper - i knew the types of relationships - but you explained it well - exactly how i would have explained it..