oracle stored procedure paging

In order to better optimize database query performance, using stored procedures for paging queries is a good choice. Establishing a stored procedure allows us to consume resources on paging when querying large amounts of data. Oracle database provides several feasible advanced algorithms for paging operations, using the minimum percentage to retrieve the required results and improve query efficiency.

In Oracle, stored procedures are database objects that can be used to precompile and save SQL statements. Stored procedures can accept parameters and return results. When processing large amounts of data, using stored procedures can greatly improve database query efficiency.

Below, we will introduce how to implement paging query through stored procedures in Oracle.

First, we need to set the parameters of the stored procedure so that it can be paginated.

 CREATE OR REPLACE PROCEDURE paged_results(
  in_table IN VARCHAR2,
  in_where IN VARCHAR2 DEFAULT NULL,
  in_orderby IN VARCHAR2 DEFAULT NULL,
  in_pageSize IN NUMBER DEFAULT 10,
  in_pageNumber IN NUMBER DEFAULT 1,
  out_cursor OUT SYS_REFCURSOR) AS

This stored procedure accepts five input parameters: table name, query conditions, sorting conditions, number of records displayed on each page, and page number. Among them, the in_table, in_pageSize and in_pageNumber parameters must be filled in, while the in_where and in_orderby parameters are optional. out_cursor is used as the output parameter to obtain the query results of each page.

Next, we have to consider how to paginate in the stored procedure, which is the key to our functionality.

We can use another stored procedure to implement paging. As shown below, through the FOR LOOP loop, the records contained in the specified page in the data set are retrieved, and the number of records to be returned is calculated.

cnt := in_pageSize * ( in_pageNumber - 1 );
v_sql := 'select count(*) from ' || in_table ||
         '' || NVL( in_where, '' ) || '';
EXECUTE IMMEDIATE v_sql INTO v_totalRows;
v_totalPages := CEIL( v_totalRows / in_pageSize );
v_currentPage := in_pageNumber;
v_rowCount := 0;
v_startRow := 1;
v_endRow := in_pageSize;
OPEN out_cursor FOR
( SELECT *
  FROM
  (SELECT
    ROW_NUMBER() OVER(ORDER BY tmp_table.row_counter) row_num,
    tmp_table.*
  FROM
    (SELECT
      ROWNUM - 1 + cnt row_counter,
      t.*
    FROM
      ( SELECT
          *
        FROM ' || in_table || 
          NVL( in_where, '' ) ||
          NVL( in_orderby, '' ) || '
      )t
    WHERE
      ROWNUM <= cnt + in_pageSize
    ) tmp_table
  WHERE
    tmp_table.row_counter >= cnt
  )
);

This stored procedure will return the paging results of the specified page number. The two parameters in_where and in_orderby are used to control the conditions and sorting method. If the in_where and in_orderby parameters are not passed, it means no condition or ordering is required.

In the for loop, we first retrieve the number of records that meet the conditions in the entire data set, and then calculate the total number of pages based on the number of records displayed on each page. Next, we retrieve the data in the specified page. Here we use Row_num and row_counter are eliminated, row_num represents the row number, and row_counter is the total number of rows counted sequentially. Finally, we open the cursor and return the paginated result set.

In the stored procedure, in order to facilitate processing, we use the EXECUTE IMMEDIATE statement to dynamically execute the SQL statement, so we need to set the v_sql parameter to dynamically receive the SQL statement. In addition, four common variables need to be defined to save the current page number, total number of pages, starting line and ending line.

After executing the above steps, Oracle will be able to process the paging logic normally. Now we can call the stored procedure in PL/SQL to retrieve the data.

 DECLARE
  CURSOR c_results IS
    SELECT *
      FROM table_name;
  v_result sds.table_name%ROWTYPE;
  in_pageNum NUMBER := 50;
  in_pageSize NUMBER := 10;
  in_orderBy VARCHAR2(100) := ” ORDER BY column_2 ASC”;
  v_string VARCHAR2(100);
  new_cursor SYS_REFCURSOR;
BEGIN
  sds.paged_results(
    in_table_name => 'table_name',
    in_where => 'WHERE column_1 < 50',
    in_orderBy => in_orderBy,
    in_pageSize => in_pageSize,
    in_pageNum => in_pageNum,
    out_cursor => new_cursor);
END;

Through the calling method in the above example, we can easily retrieve the data of the specified page and return the result set as an output parameter. Among them, in_where and in_orderBy can provide conditions for your data range and sorting method.

In general, using stored procedures for paging can improve database performance when querying large amounts of data. What we need to note is that the operating efficiency of stored procedures is related to the quality of SQL writing, and must be adjusted and optimized according to specific conditions.

Through the above examples, I believe everyone has understood that the basic principle of using stored procedures to implement paging queries is to dynamically generate SQL statements to implement paging by setting paging parameters. Using stored procedures can effectively alleviate the burden of database queries, improve database query efficiency, and reduce the number of server-side requests.

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