Database relationships
Database relationships are associations between tables that are created using join statements to retrieve data.
The following table describes the database relationships.
| Type of relationship | Description |
|---|---|
| One-to-one | Both tables can have only one record on each side of the relationship. Each primary key value relates to none or only one record in the related table. Most one-to-one relationships are forced by business rules and do not flow naturally from the data. Without such a rule, you can typically combine both tables without breaking any normalization rules. |
| One-to-many | The primary key table contains only one record that relates to none, one, or many records in the related table. |
| Many-to-many | Each record in both tables can relate to none or any number of records in the other table. These relationships require a third table, called an associate or linking table, because relational systems cannot directly accommodate the relationship. |
In the Database Configuration application, you can define Structured Query Language (SQL) statements for joins, and create relationships between parent and child objects. You can use a join to link data from multiple objects. The parent is the existing object and the child is the object that you are create.
Example
Parent = MAXUSER, Child =SITE, and Name = DEFSITE means that maxuser exists and you want to get the site for the default site for the user.
siteid = :defsite
This
configuration means site.siteid = maxuser.defsite.
When the SQL statement is run, the value of the parent attribute replaces
anything preceded by a colon.