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How to define relationships between databases
1 to 1
many to many
1 to many
RE: How to define relationships between databases
Hi Jonathan
The relationships between tables are typically defined by the data in the tables. When you link a common field between two tables, then the relationship type is created.
One-to-One
So if you have two tables that will only ever contain one record relating to one record, then you will have a one-to-one relationship. It is unusual to have a separate table for a one-to-one relationship, as usually you would just have an additional field in the table.
One-to-Many
This is the most common type of relationship between any two tables. An example could be - one store, many products, etc.
Many-to-Many
This type of relationship requires an interlinking table to match the relationship of the two other tables. For example, several clients making several purchases, over a period of time. The client would come back an make another purchase. One table would contain the Client info, the other table the Product info. The interlinking table would be a Sales table of sorts and would record when the client came in, what there details are and what they pruchased.
Does that make sense?
Regards
Richard
