How to implement paging in oracle

Steps to implement paging: 1. Use ROWNUM for paging query; 2. Set paging parameters before executing the query; 3. Use the "COUNT(*)" function to get the total number of rows, and use "CEIL" function to round up to calculate the total number of pages; 4. Use the "WHERE" clause in the external query to filter out a specific row number range to implement paging queries.

In the Oracle database, you can use ROWNUM and paging queries to implement the paging function. ROWNUM is a pseudo column provided by Oracle, which is used to assign a unique row number to each row of query results. Using the combination of ROWNUM and paging queries, we can obtain specific data based on the specified number of pages and the number of rows displayed on each page.

The following is a common method to implement paging in Oracle:

1. Use ROWNUM for paging query:

First, we need to write A basic query statement to get all the data, and then perform paging operations on this basis. For example, we have a table named "employees" that contains employee information, and we want to perform a paging query based on the employee's ID.

   SELECT *
   FROM (
       SELECT e.*, ROWNUM AS rn
       FROM employees e
       ORDER BY e.employee_id
   )
   WHERE rn BETWEEN :start_row AND :end_row;

In the above query statement, we use ROWNUM as a pseudo column with the alias "rn", which represents the row number of each row. Then, we make this query as a subquery and use the "WHERE" clause in the outer query to filter out a specific range of row numbers to implement a paging query.

2. Set paging parameters:

In the above query statement, we use two parameters ":start_row" and ":end_row" to represent each page Starting line number and ending line number. These parameters need to be set before executing the query. For example, if we want to get the first page of data and display 10 rows per page, we can set ":start_row" to 1 and ":end_row" to 10.

3. Calculate the total number of pages:

In order to achieve a better paging experience, it is usually necessary to calculate the total number of pages. We can use the following query statement to get the total number of rows and total pages:

   SELECT COUNT(*) AS total_rows, CEIL(COUNT(*) / :page_size) AS total_pages
   FROM employees;

In the above query statement, we use the "COUNT(*)" function to get the total number of rows, and the "CEIL" function to Round up to calculate the total number of pages. The ":page_size" parameter indicates the number of rows displayed on each page.

4. Complete paging query example:

The following is a complete example demonstrating how to implement paging query in Oracle:

   -- 设置分页参数
   :start_row := (:page_number - 1) * :page_size + 1;
   :end_row := :page_number * :page_size;
   -- 执行分页查询
   SELECT *
   FROM (
       SELECT e.*, ROWNUM AS rn
       FROM employees e
       ORDER BY e.employee_id
   )
   WHERE rn BETWEEN :start_row AND :end_row;
   -- 计算总页数
   SELECT COUNT(*) AS total_rows, CEIL(COUNT(*) / :page_size) AS total_pages
   FROM employees;

In In the above example, we use the ":page_number" parameter to indicate the number of pages to be obtained. First, we calculate the values ​​of the ":start_row" and ":end_row" parameters based on the ":page_number" and ":page_size" parameters, and then execute the paging query. Finally, we use another query to calculate the total number of rows and total pages.

Summary:

By using ROWNUM and paging queries, we can implement paging functionality in Oracle database. First, we need to write a basic query statement and use ROWNUM as a pseudo column to assign a unique row number to each row. Then, we make this query as a subquery and use the "WHERE" clause in the outer query to filter out a specific range of row numbers to implement a paging query. In addition, we can also set paging parameters and calculate the total number of pages to provide a better paging experience.

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