ROWNUM, Cursor, and Paged Reports

Question

I am using ASP against a Oracle 8i DB in a web application. I have some large reports (approx 2,000 records) that I need to display on the site in a paged style report. i.e. 25 records on page 1, 26-50 on page 2, etc...... Much like you see here at OTN in the forums.
The problem is that when I go through the the ADO to build my recordset against the DB, I need to be able to select just a certain set of rownumbers. I will also need to be able to reorder the report based on client response. I know that the ROWNUM psudeofield is filled before any sort criteria is applied through the order by clause. So if I select against the view, how will I tell it to give me the next set of records that will make up my page. A oracle book I have says to use the cursor object to do this, but I am not really familiar with that, and from what I can see, it still didn't tell me how to select just a small part of the overall recordset that might be returned to the cursor by the SQL statement.
Does any of this make sense? And if so, can someone please point me to a good source of information on how to do this. I know it has to be possible, becuase sites have that ability all over the place, but as I might be changing from ASP to JSP soon, I don't really want to do it all in code,becuase then I have to rewrite that as well. Doing this on the database is really my only good option.

Answer 1

Here is an example, that uses the Oracle emp demo table to demonstrate how to use a ref cursor to return a result set ordered by whatever columns you want and get any set of rows you want. In the example, I first ordered by the empno column and retrieved the first 10 rows, then the next set of 10 rows (there are only 14 rows, so it just displays 4 more rows). Then I ordered by the ename column and retrieved 5 rows at a time. You can specify any number or combination of columns and any starting or ending rows you want.
SQL> CREATE OR REPLACE PACKAGE package_name
  2  AS
  3    TYPE cursor_type IS REF CURSOR;
  4    PROCEDURE procedure_name
  5      (p_result_set    IN OUT cursor_type,
  6       p_order_by      IN     VARCHAR2,
  7       p_start_row     IN     NUMBER,
  8       p_end_row       IN     NUMBER);
  9  END package_name;
10  /
Package created.
SQL> CREATE OR REPLACE PACKAGE BODY package_name
  2  AS
  3    PROCEDURE procedure_name
  4      (p_result_set    IN OUT cursor_type,
  5       p_order_by      IN     VARCHAR2,
  6       p_start_row     IN     NUMBER,
  7       p_end_row       IN     NUMBER)
  8    IS
  9      v_sql                   VARCHAR2 (4000);
10    BEGIN
11      v_sql :=
12          'SELECT *'
13      || ' FROM   (SELECT ROWNUM AS r, a.*'
14      ||         ' FROM   (SELECT   * '
15      ||                 ' FROM     emp'
16      ||                 ' ORDER BY ' || p_order_by || ') a'
17      ||         ' WHERE  ROWNUM <= :p_end_row )'
18      || ' WHERE    r >= :p_start_row';
19      OPEN p_result_set FOR v_sql USING p_end_row, p_start_row;
20    END procedure_name;
21  END package_name;
22  /
Package body created.
SQL> SET LINESIZE 125
SQL> VARIABLE g_ref REFCURSOR
SQL> -- to get first ten rows ordered by empno:
SQL> EXEC package_name.procedure_name (:g_ref, 'EMPNO', 1, 10)
PL/SQL procedure successfully completed.
SQL> PRINT g_ref
         R      EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM     DEPTNO
         1       7369 SMITH      CLERK           7902 17-DEC-80        800                    20
         2       7499 ALLEN      SALESMAN        7698 20-FEB-81       1600        300         30
         3       7521 WARD       SALESMAN        7698 22-FEB-81       1250     505.07         30
         4       7566 JONES      MANAGER         7839 02-APR-81       2975                    20
         5       7654 MARTIN     SALESMAN        7698 28-SEP-81       1250       1400         30
         6       7698 BLAKE      MANAGER         7839 01-MAY-81       2850                    30
         7       7782 CLARK      MANAGER         7839 09-JUN-81       2450                    10
         8       7788 SCOTT      ANALYST         7566 09-DEC-82       3000                    20
         9       7839 KING       PRESIDENT            17-NOV-81       5000                    10
        10       7844 TURNER     SALESMAN        7698 08-SEP-81       1500          0         30
10 rows selected.
SQL> -- to get second ten rows ordered by empno:
SQL> EXEC package_name.procedure_name (:g_ref, 'EMPNO', 11, 20)
PL/SQL procedure successfully completed.
SQL> PRINT g_ref
         R      EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM     DEPTNO
        11       7876 ADAMS      CLERK           7788 12-JAN-83       1100                    20
        12       7900 JAMES      CLERK           7698 03-DEC-81        950                    30
        13       7902 FORD       ANALYST         7566 03-DEC-81       3000                    20
        14       7934 MILLER     CLERK           7782 23-JAN-82       1300                    10
SQL> -- to get first five rows ordered by ename:
SQL> EXEC package_name.procedure_name (:g_ref, 'ENAME', 1, 5)
PL/SQL procedure successfully completed.
SQL> PRINT g_ref
         R      EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM     DEPTNO
         1       7876 ADAMS      CLERK           7788 12-JAN-83       1100                    20
         2       7499 ALLEN      SALESMAN        7698 20-FEB-81       1600        300         30
         3       7698 BLAKE      MANAGER         7839 01-MAY-81       2850                    30
         4       7782 CLARK      MANAGER         7839 09-JUN-81       2450                    10
         5       7902 FORD       ANALYST         7566 03-DEC-81       3000                    20
SQL> -- to get second five rows ordered by ename:
SQL> EXEC package_name.procedure_name (:g_ref, 'ENAME', 6, 10)
PL/SQL procedure successfully completed.
SQL> PRINT g_ref
         R      EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM     DEPTNO
         6       7900 JAMES      CLERK           7698 03-DEC-81        950                    30
         7       7566 JONES      MANAGER         7839 02-APR-81       2975                    20
         8       7839 KING       PRESIDENT            17-NOV-81       5000                    10
         9       7654 MARTIN     SALESMAN        7698 28-SEP-81       1250       1400         30
        10       7934 MILLER     CLERK           7782 23-JAN-82       1300                    10
SQL> -- to get third set of five rows ordered by ename:
SQL> EXEC package_name.procedure_name (:g_ref, 'ENAME', 11, 15)
PL/SQL procedure successfully completed.
SQL> PRINT g_ref
         R      EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM     DEPTNO
        11       7788 SCOTT      ANALYST         7566 09-DEC-82       3000                    20
        12       7369 SMITH      CLERK           7902 17-DEC-80        800                    20
        13       7844 TURNER     SALESMAN        7698 08-SEP-81       1500          0         30
        14       7521 WARD       SALESMAN        7698 22-FEB-81       1250     505.07         30