What Is User-Defined Data Type in Oracle?


Larry Thompson

What Is User-Defined Data Type in Oracle?

Oracle allows users to define their own data types called User-Defined Data Types (UDDTs). These custom data types can be created using the CREATE TYPE statement.

UDDTs provide a way to encapsulate complex data structures and behaviors into a single entity, making them more manageable and reusable.

Advantages of User-Defined Data Types

Using UDDTs offers several advantages in database design and development. Let’s explore some of these benefits:

1. Modularity and Reusability:

UDDTs promote modularity by allowing users to encapsulate related attributes and methods into a single object. This not only makes the code more organized but also enhances reusability.

Once a UDDT is defined, it can be used in multiple tables, reducing redundancy and improving maintainability.

2. Abstraction:

UDDTs provide a level of abstraction by hiding the implementation details of complex data structures. With an appropriate name for the UDDT, other developers can easily understand its purpose without delving into its internal structure.

This abstraction simplifies the codebase and improves readability.

3. Consistency:

By defining UDDTs, you can enforce consistent data structures across different tables in your database schema. This ensures that related entities have the same attributes and methods, facilitating better data integrity and reducing errors caused by inconsistent data definitions.

Creating a User-Defined Data Type in Oracle

To create a UDDT in Oracle, you can use the CREATE TYPE statement. Here’s an example that demonstrates the syntax:

CREATE TYPE employee_type AS OBJECT (
  employee_id NUMBER,
  first_name VARCHAR2(50),
  last_name VARCHAR2(50),
  hire_date DATE

In the above example, we define a UDDT called employee_type with four attributes: employee_id, first_name, last_name, and hire_date. These attributes have their respective data types defined.

Using User-Defined Data Types in Tables

Once you have defined a UDDT, you can use it as a column type in your tables. Here’s an example of creating a table that uses the previously defined employee_type:

CREATE TABLE employees (
  emp_data employee_type

In this example, the emp_data column is of type employee_type. This allows storing complex employee data within this single column.

Nested Table Types:

Oracle also supports creating nested table types using UDDTs. A nested table is a collection of elements of the same UDDT. Here’s an example:

CREATE TYPE contact_type AS OBJECT (
  name VARCHAR2(50),
  emails phone_numbers,
  phone_numbers phone_numbers
CREATE TABLE contacts (
  contact_id NUMBER PRIMARY KEY,
  contact_data contact_type

In this example, we define two UDDTs: phone_numbers, which is used to store a collection of phone numbers, and contact_type, which encapsulates a person’s name along with their email addresses and phone numbers.


User-Defined Data Types in Oracle provide a powerful way to encapsulate complex data structures and behaviors. They promote modularity, reusability, abstraction, and consistency in database design.

By creating custom data types, you can enhance the organization and maintainability of your codebase. So, go ahead and leverage the power of UDDTs in your Oracle projects!

Discord Server - Web Server - Private Server - DNS Server - Object-Oriented Programming - Scripting - Data Types - Data Structures

Privacy Policy