Foreign key - Wikipedia
This Oracle tutorial explains how to use Foreign Keys in Oracle with syntax and The foreign key in the child table will generally reference a primary key in the. Course_objtyp (PRIMARY KEY (CourseID), FOREIGN KEY (DeptID) REFERENCES Department_objtab(DeptID), FOREIGN KEY (TeacherID) REFERENCES. This is the table that contains the primary key that your new foreign key will link to . For example, if you Foreign Key Relation Across Database.
This is done by declaring a constraint after all of your columns have been declared. The advantage of this method is that you can give your foreign key constraint a name, which is helpful for altering, enabling, and disabling it at a later date.
Using the inline method, a name is generated automatically by the Oracle database.SQL: Foreign Key Creation
The syntax for creating a foreign key using the out-of-line method is: This denotes that you will be defining a constraint. Next, provide a name for your new constraint. This can be up to 30 characters. I prefer to stick to a standard when naming my constraints, so I start the names with fk. Then, open brackets and add in the name of the column in this table that will be the foreign key. Then, close the brackets.
Then, open the brackets, add in the name of the column in the other table in this case, the department tableand then close the brackets. Finally, close the brackets to the create table statement and add a semicolon.
The statement is now ready to run. The foreign key will be created with the name you have specified. Target foreign keys normally occur in bidirectional one-to-one mappings, because one side has a foreign key and the other shares the same foreign key in the other's table. Target foreign keys can also occur when large cascaded composite primary keys exist that is, one object's primary key is composed of the primary key of many other objects.
Working with Foreign Keys
In this case it is possible to have a one-to-one mapping that contains both foreign keys and target foreign keys. In a target foreign key, it does not.
When mapping a relationship, you must understand these differences between a foreign key and a target foreign key, to ensure that the relationship is defined correctly. In a bidirectional relationship where the two classes in the relationship reference each other, only one of the mappings should have a foreign key.
- Oracle Foreign Key
- Working with One-to-One Mappings
- Foreign key
The other mapping should have a target foreign key. If one of the mappings in a bidirectional relationship is a one-to-many mapping, see "Working with Variable One-to-One Mappings" for details.
Oracle / PLSQL: Foreign Keys
Creating One-to-One Mappings Use this procedure to create a one-to-one mapping. To create a one-to-one mapping: In the Navigator pane, select the mapping to be mapped and click the One-to-One Mapping button on the mapping toolbar. The One-to-one mapping tab appears in the Editor pane.
You can also specify: Field Description Table Reference Use the drop-down list to choose a table reference for the mapping. Click New to create a new table Key Pairs Use the drop-down list to choose a field from the source table. Target Field Use the drop-down list to choose a field from the target table.