Structured type

SQL examples

Object structured type

In order to define a custom structure type using Oracle database one could use statements such as these:

CREATE TYPE Person_Type AS OBJECT (
    person_title VARCHAR2(10),
    person_first_name VARCHAR2(20),
    person_last_name VARCHAR2(20),
) 
NOT FINAL;

Such structure type can be then used to create a table that would also hold all columns defined in Person_Type:

CREATE TABLE Person_Table OF Person_Type;

Custom structure types support inheritance, which means that one can create another type that inherits from previous. NOT FINAL statement must be however included in a base structure type definition in order to allow for creation of any other subtypes.

CREATE TYPE Student_Type UNDER Person_Type (
    matriculation_number NUMBER(10)
);

Student_Type then could be used in order to create a Student_Table which will include all columns defined in Person_Type as well. Primary Key and Constraints should be defined during or after creation of table and cannot be defined inside structure type itself.

CREATE TABLE Student_Table OF Student_Type (
  matriculation_number PRIMARY KEY,
  CONSTRAINT person_title_not_null_constraint NOT NULL (person_title),
);

Each custom structure type can also contain other types in order to support more complex structures:

CREATE TYPE Address_Type AS OBJECT (
    address_street VARCHAR2(30),
    address_city VARCHAR2(30),
);

CREATE TYPE University AS OBJECT (
    university_name VARCHAR2(30),
    university_address Address_Type
);

Further reading

• Jim Melton (2003). Advanced SQL: 1999. Morgan Kaufmann. ISBN 978-1-55860-677-7. Chapters 2-4.
• Suzanne W. Dietrich; Susan D. Urban (2011). Fundamentals of Object Databases: Object-Oriented and Object-Relational Design. Morgan & Claypool Publishers. ISBN 978-1-60845-476-1. Chapter 3.
• Catherine Ricardo (2011). Databases Illuminated (2nd ed.). Jones & Bartlett Publishers. ISBN 978-1-4496-0600-8. Chapter 8.

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