Oracle pagination with order by field not unique performance
It's also wrong, because now you are getting 500 rows (could be ANY 500 rows) and then sorting them.  If L_DATE is not sufficient to give a deterministic answer, you do need to add more columns.  The most obvious choice would be a primary key column:

SELECT *
FROM (
    SELECT XX.*, ROWNUM AS RN
    FROM (
        SELECT *
        FROM T_LOG
        WHERE OP_TYPE = 'Q' ORDER BY L_DATE, SOME_PK_COL
    ) XX
    WHERE ROWNUM &lt;= 500
) XXX
WHERE RN &gt; 0;


...so that in the absence of good information in L_DATE (or whatever column is nominated by the user), you will be sorting on something deterministic.

Also: If you do select ... from table where rownum &lt;= 10 then the 10 rows you get back is not deterministic over time.  There is no predefined order to the rows.