Need advice on pagination query

Question

Hello,
I have the following example of a pagination query, but I heard that there might be some drawbacks to this query. Could anyone please let me know any problems that might happen with this? The user will provide inputs for p and q. Thanks.
Select *
From (select rownum as n, * from table order by x, y, z)
Where n between p and q

Answer 1

Hi,
arizona9952 wrote:
Hello,
I have the following example of a pagination query, but I heard that there might be some drawbacks to this query. Could anyone please let me know any problems that might happen with this? The user will provide inputs for p and q. Thanks.
Select *
From (select rownum as n, * from table order by x, y, z)
Where n between p and qIf there is anything in the SELECT clause along with *, then * has to be qualified by a table name or alias. (See the example below.)
ORDER BY is applied after ROWNUM is assigned. For example, the qub-query might find x values 5, 8 and 3, and assign ROWNUM in that order, so you'd have
x   ROWNUM
5   1
8   2
3   3so if you were looking for the 2nd highest, you would get 8.
I would use the analytic ROW_NUMBER function instead of ROWNUM.
WITH  got_r_num      AS
     SELECT  x.*     -- not just *
     ,     ROW_NUMBER () OVER (ORDER BY x, y, z)  AS r_num
     FROM     table_x
SELECT       *
FROM       got_r_num
WHERE       r_num     BETWEEN  :p
            AND      :Q
ORDER BY  r_num
;To use ROWNUM, you would need 2 sub-queries. In the first, you would use ORDER BY, in the second, apply ROWNUM, and finally, in the main query, pick the values you wanted.