HELP: I am totally fooled by searching result. IT IS WEIRD!

Question

Hi everyone,
It is a very simple query then SQL retrieves partial results to me.
Please see deails as follows;
The statement 1 shows 4 records in period 9 when I searching period >=9,
HOW COME it only shows 2 records in statement 2 that I searched period =9
has anyone met such searching result like me? It looks SQL retrieving partial records????
Oracle V10.2.0.4.0
********statement 1: *******************************
SELECT * FROM WA_INVENTORY_VALUATION_RPT
WHERE COMPANY='3R' and YEAR=2009 and period >=9
order by period ;
********RESULT: 4 records in period 9*******************
COMPANY     YEAR     PERIOD     OWNERSHIP     TRANSACTION     DESCRIPTION     AMOUNT     TYPE
3R     2009     9     FGOODS          Opening Balance     154115.77     1
3R     2009     9     PARTS          Opening Balance     119985.4     1
3R     2009     9     PARTS          Closing Balance     123855.48     3
3R     2009     9     FGOODS          Closing Balance     194303.77     3
3R     2009     10     FGOODS          Opening Balance     194303.77     1
3R     2009     10     PARTS          Opening Balance     123855.48     1
3R     2009     10     FGOODS          Closing Balance     155746.77     3
3R     2009     10     PARTS          Closing Balance     120223.44     3
3R     2009     11     PARTS          Closing Balance     121156.71     3
3R     2009     11     PARTS          Opening Balance     120223.44     1
*********statement 2***************************
SELECT * FROM WA_INVENTORY_VALUATION_RPT
WHERE COMPANY='3R' and YEAR=2009 and period =9
order by period ;
******** RESULT: 2 records in period 9 *************
COMPANY     YEAR     PERIOD     OWNERSHIP     TRANSACTION     DESCRIPTION     AMOUNT     TYPE
3R     2009     9     PARTS          Opening Balance     119985.4     1
3R     2009     9     FGOODS          Opening Balance     154115.77     1
************TABLE STRUCTURE******************
Column Name     ID     Data Type     Null?
COMPANY     1     VARCHAR2 (20 Byte)     Y
YEAR     2     NUMBER     Y
PERIOD     3     NUMBER     Y
OWNERSHIP     4     VARCHAR2 (6 Byte)     Y
TRANSACTION     5     CHAR (1 Byte)     Y
DESCRIPTION     6     CHAR (15 Byte)     Y
AMOUNT     7     NUMBER     Y
TYPE     8     CHAR (1 Byte)     Y
Edited by: user2544957 on 16/09/2009 16:31

Answer 1

Thanks for your reply. Please see data structure as follows;
Column Name     ID     Data Type     Null?
COMPANY     1     VARCHAR2 (20 Byte)     Y
YEAR     2     NUMBER     Y
PERIOD     3     NUMBER     Y
OWNERSHIP     4     VARCHAR2 (6 Byte)     Y
TRANSACTION     5     CHAR (1 Byte)     Y
DESCRIPTION     6     CHAR (15 Byte)     Y
AMOUNT     7     NUMBER     Y
TYPE     8     CHAR (1 Byte)     Y