In Web development, putting too many records from the database into the Web server is memory intensive processing. This is where the concept of paging comes form. At any point in time, you display only a few records to the user (for ex. 10 no.). This is helpful if the Web site has a lot of hits. A typical scenario is that the query returns 100 rows, but you are going to display only records from 20 to 30. Why load all 100 into the Web server?
Here is the query in the Oracle database to take only those 10 records:
SELECT emp_no, salaryFROM(SELECT ROWNUM R, A.* FROM(select empno,salary from employee order by salary desc) A)WHERE R BETWEEN 20 and 29
The above query will return 10 rows, assuming the employee table exists with the required columns.