Examples to explain how to use Oracle stored procedures to implement paging queries

In Oracle database, stored procedures can be used to implement many complex logics, among which paging queries are also one of the common requirements. This article will introduce how to use Oracle stored procedures to implement paging queries and provide an example.

1. Requirements for paging query

In actual applications, it is usually necessary to query and display a large amount of data. If all data is displayed at once, it will not only affect system performance, but also cause poor user experience. Therefore, we usually need to display the data in pages and display the data page by page.

In Oracle database, paging queries are usually implemented using the ROWNUM keyword. For example, to query the first 10 records in the database, you can use the following query statement:

SELECT *
FROM table_name
WHERE ROWNUM <= 10;

This query statement can return the first 10 data in the table and implement simple paging query. But when you need to query the 11th to 20th data, you need to use a more complex query statement:

SELECT *
FROM (
  SELECT ROWNUM rn, t.*
  FROM (
    SELECT *
    FROM table_name
    ORDER BY field_name
  ) t
  WHERE ROWNUM <= 20
)
WHERE rn >= 11;

This query statement can return the 11th to 20th data in the table. However, this query statement is relatively complex and not very readable. If there are many places where paging queries are required, many such query statements need to be written, which is not convenient for maintenance and management.

In order to solve this problem, we can use Oracle stored procedures to implement the paging query function.

2. Use stored procedures to implement paging query

Use stored procedures to implement paging query function, mainly by passing parameters. We need to pass the following parameters:

• Table name;
• Column to be displayed;
• Sort field;
• Page;
• The number of records displayed on each page.

Based on these parameters, the stored procedure can implement paging queries based on the ROWNUM keyword.

The following is an example of using a stored procedure to implement paging query:

CREATE OR REPLACE PROCEDURE get_page_data(
    p_table_name IN VARCHAR2,
    p_columns IN VARCHAR2,
    p_order_by IN VARCHAR2,
    p_page_num IN NUMBER,
    p_page_size IN NUMBER,
    p_result OUT SYS_REFCURSOR
)
IS
BEGIN
    OPEN p_result FOR
        SELECT *
        FROM (
            SELECT ROWNUM rn, t.*
            FROM (
                SELECT p_columns
                FROM p_table_name
                ORDER BY p_order_by
            ) t
            WHERE ROWNUM <= p_page_num * p_page_size
        )
        WHERE rn >= (p_page_num - 1) * p_page_size + 1;
END;
/

In this stored procedure, the SYS_REFCURSOR type is used to return query results. Then, a paging query statement is generated based on the passed parameters, and finally the query results are put into the returned result set.

When calling this stored procedure, you can use the following query:

DECLARE
    v_result SYS_REFCURSOR;
BEGIN
    get_page_data('table_name', '*', 'field_name', 2, 10, v_result);
END;
/

This query will return the data on page 2 of the table, with 10 records displayed on each page.

In short, using stored procedures can easily implement the paging query function, making the code clearer, easier to understand, and more maintainable. The above example has provided an idea that can be modified and expanded according to actual needs.

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