how to use limit keyword in oracle - mysql

Question

I am retrieving data from table but instead of all row, I want 20 rows at a time for pagination. For this I use limit keyword which work perfectly in Mysql but not in Oracle.
Code:
"select "+ "C.CONTRACTOR_ID,C.CONTRACTOR_NAME,nvl(C.CONTACT_PERSON_1,'-'),nvl(C.CONTACT_PERSON_2,'-'),C.REGISTRATION_NO,CRA.DESCRIPTION REG_AUTH_NAME,"+
"to_char(C.VALID_FROM,'dd/mm/yyyy'),to_char(C.VALID_TO,'dd/mm/yyyy'),CC.DESCRIPTION CONTRACTOR_CLASS,C.INCORP_PLACE,"+
"IT.DESCRIPTION INCORP_TYPE,nvl(to_char(C.DATE_OF_INCORP,'dd/mm/yyyy'),'-') DATE_OF_INCORP,C.ADDRESS1,nvl(C.ADDRESS2,'-'),nvl(C.EMAIL_ID,'-'),"+
"nvl(C.WEBSITE_URL,'-'),nvl(C.PHONE_NO,'-'),nvl(C.FAX_NO,'-'),nvl(C.MOBILE_NO,'-'),C.BANK_NAME,C.BANK_BRANCH,C.ACCOUNT_NO,C.IFSC_CODE," +
"C.PAN_NO,nvl(C.TIN_NO,'-'),nvl(C.CST_NO,'-') "+
"from "+
"CONTRACTOR C "+
"inner join CONTRACTOR_REG_AUTH CRA on CRA.REG_AUTH_ID=C.REG_AUTH_ID "+
"inner join CONTRACTOR_CLASS CC on CC.CLASS_ID=C.CONTRACTOR_CLASS_ID "+
"inner join INCORPORATION_TYPE IT on IT.INCORP_TYPE=C.INCORP_TYPE "+
"limit " + offset + ", " + noOfRecords ";
Here no order by keyword is there. I am retrieving data from different table and then display only 20 rows at a time.

Answer 1

In Oracle, you can use the special rownum variable. This example behaves like limit FirstRow, NrOfRows:
select *
from (
select *
, rownum as rn
from YourTable
order by
id
) as SubQueryAlias
where FirstRow <= rn
and rn < FirstRow + NrOfRows
An optimized version of this query from AskTom, linked from this SO question:
select *
from (
select /*+ FIRST_ROWS(n) */
rownum as rn
, *
from (
select *
from YourTable
order by
id
) as SubQueryAlias1
where rownum <= FirstRow + NrOfRows
) as SubQueryAlias2
where rn >= FirstRow