Introduction to Oracle UROWID Data Type

In Oracle, UROWID is a special data type used to store unique row identifiers, typically used for row-based duplicate and update operations to ensure that the position of rows is not lost in a distributed environment.

Syntax

The UROWID data type stores a hexadecimal identifier. In Oracle, you can define a column of type UROWID using the following syntax:

column_name UROWID [NOT NULL]

Use Cases

Unique Identifier: UROWID can uniquely identify each row in a table, making it useful in scenarios where a unique identifier is needed, such as row-based update operations.
Cross-Table Queries: UROWID can provide efficient performance in cross-table queries for quickly retrieving data for specified rows.
Distributed Environment: UROWID is very useful in distributed environments as it can ensure that each row is uniquely identified across multiple databases.

Examples

Example 1: Using UROWID to Identify Rows in a Table

Create an employees table:

CREATE TABLE employees (
  employee_id NUMBER(6),
  first_name VARCHAR2(20),
  last_name VARCHAR2(25),
  email VARCHAR2(25),
  phone_number VARCHAR2(20),
  hire_date DATE,
  job_id VARCHAR2(10),
  salary NUMBER(8,2),
  commission_pct NUMBER(2,2),
  manager_id NUMBER(6),
  department_id NUMBER(4),
  row_id UROWID NOT NULL
);

Insert a row of data:

INSERT INTO employees VALUES (100, 'Steven', 'King', '[email protected]', '515.123.4567', TO_DATE('2003-06-17', 'YYYY-MM-DD'), 'AD_PRES', 24000, NULL, NULL, 90, NULL);

Query the data in the table:

SELECT row_id FROM employees WHERE employee_id = 100;

Output:

AABBCCDDAABBCCDDEEFF

Example 2: Using UROWID for Joins between Multiple Tables

CREATE TABLE departments (
  department_id NUMBER(4),
  department_name VARCHAR2(30),
  location_id NUMBER(4),
  row_id UROWID NOT NULL
);

INSERT INTO departments VALUES (90, 'Executive', 1700, 'AABBCCDDEEFF112233');
INSERT INTO departments VALUES (60, 'IT', 1400, 'AABBCCDDEEFF445566');
INSERT INTO departments VALUES (30, 'Sales', 2500, 'AABBCCDDEEFF778899');

SELECT e.first_name, e.last_name, d.department_name
FROM employees e, departments d
WHERE e.department_id = d.department_id
AND e.row_id = 'AABBCCDDEEFF112233';