Mastering Pagination in Oracle: Unveiling the Secrets of ROW_NUMBER() and BETWEEN

Problem: How to retrieve and display a specific subset of data from a large Oracle table, allowing users to navigate through different sections efficiently.

Solutions:

There are two main approaches to implement paging in Oracle:

Using ROW_NUMBER() and BETWEEN:

This method leverages the ROW_NUMBER() window function to assign a unique number to each row based on a specific order (e.g., chronological order). Then, the BETWEEN clause is used to select rows within the desired page range.

Example:

SELECT *
FROM (
  SELECT *, ROW_NUMBER() OVER (ORDER BY creation_date DESC) AS rn
  FROM your_table
)
WHERE rn BETWEEN :page_start AND :page_end;

Explanation:

• This query first assigns a row number (rn) to each row in the your_table table, ordered by creation_date in descending order.
• The outer query then selects all columns from the subquery, filtering based on the rn value.
• Two bind variables, :page_start and :page_end, represent the starting and ending row numbers for the desired page. These values can be passed dynamically based on user input or calculated using page size and current page number.

Using a Stored Procedure:

Stored procedures offer a more encapsulated and reusable approach to paging. They can encapsulate the paging logic and accept parameters like page size and current page number, returning the desired data subset.

Example (simplified):

CREATE OR REPLACE PROCEDURE get_page(
  p_page_size IN NUMBER,
  p_current_page IN NUMBER,
  CURSOR c_data OUT your_table%TYPE
)
IS
  l_start_row NUMBER;
BEGIN
  l_start_row := (p_current_page - 1) * p_page_size + 1;
  OPEN c_data FOR
    SELECT *
    FROM your_table
    OFFSET l_start_row ROWS FETCH NEXT p_page_size ROWS ONLY;
END;
/

• This stored procedure takes three parameters:
  • p_page_size: The number of rows per page.
  • p_current_page: The current page number requested by the user.
  • c_data: An output cursor that will hold the data for the requested page.
• The procedure calculates the starting row number based on the page size and current page.
• It then opens a cursor and fetches the desired data using the OFFSET and FETCH NEXT clauses.

Related Issues and Solutions:

• Performance: For large datasets, optimizing queries and using appropriate indexes can significantly improve paging performance.
• Total pages calculation: To display navigation elements like "next page" and "previous page," you need to calculate the total number of pages. This can be done by querying the total number of rows in the table and dividing by the page size.
• User Interface: Integrating paging functionality with your application's user interface (UI) requires sending page requests and displaying the retrieved data. This can be done through various techniques depending on your chosen programming language and framework.