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Relationships

General

Relationship is a link between a pair of tables. It exists if two tables are linked by primary key and foreign key Each relationship is described by the type of relationship which exists between two tables, the type of participation and the degree of participation these tables.

one-to-one relationship

It occurs when a single record from the table A is precisely linked with only one record from table B and vice versa.

one-to-many relationship

It occurs when a single record from the table A may correspond to one or more records of table B, but with a single record table B corresponds to a maximum of one record in table A. It is not so mutual relationship as in the case of one-to-one.

identyfying relationships

Foreign key, which is a component of complex primary key in the dependent relation is defined as the primary foreign key and so constructed tie is named as identyfing relation

many-to-many relationship

It occurs when one record from table A is linked with many records from table B and one of the records from table B is linked with many records from table A [ wróć na górę strony ]