Create virtual rows

create virtual rows:

The query will run for first level. Then it will see, still it is less than 10, so it will try for next level and so on....

SELECT * FROM (SELECT LEVEL FROM DUAL CONNECT BY LEVEL <= 10) ;

Good Link which explains how it works:
SQL Snippets: Integer Series Generators - CONNECT BY LEVEL Method


Another way to create virtual rows is to select from ALL_OBJECTS
One more way to create virtual table:
WITH t AS
(
SELECT '01-MAR-2008' Dt FROM DUAL
UNION ALL
SELECT '02-MAR-2008' Dt FROM DUAL
UNION ALL
SELECT '03-MAR-2008' Dt FROM DUAL
UNION ALL
SELECT '04-MAR-2008' Dt FROM DUAL
)
SELECT * FROM t ;

Query to Calculate Business Days [Query to calculate date difference excluding Saturday/Sunday]
SELECT SUM(DECODE(TO_CHAR(TO_DATE('01-MAR-2008')+ROWNUM-1, 'DY'),'SUN',0,'SAT',0,1))
FROM all_objects
WHERE ROWNUM <= TO_DATE('20-MAR-2008') - TO_DATE('01-MAR-2008') + 1

Query to find Next Date and Previous date in table of current date
WITH t AS
(
SELECT '01-MAR-2008' Dt FROM DUAL
UNION ALL
SELECT '02-MAR-2008' Dt FROM DUAL
UNION ALL
SELECT '03-MAR-2008' Dt FROM DUAL
UNION ALL
SELECT '04-MAR-2008' Dt FROM DUAL
)
SELECT LEAD(Dt,1) OVER (ORDER BY dt) NEXT_DT, LAG(Dt,1) OVER (ORDER BY dt) PREV_DT
FROM t ;