SELECT   t.institution icode, c.name inst,
       SUM(ROUND(t.income * (i.income_fraction / 100),2)) inc,
       SUM(ROUND(t.wtpaid * (i.income_fraction / 100),2)) rwtpaid,
       SUM( irtn.withholding_tax_on_income
                    (t.income
                    ,i.income_fraction
                    ,i.interest_tax_rate)) tax,
       SUM(irtn.withholding_tax_balance_to_pay
                    (t.income
                    ,i.income_fraction
                    ,i.interest_tax_rate
                    ,t.wtpaid)) taxtopay 
		    FROM  
            (SELECT 
		t.institution institution, 
		t.investor investor, 
		    SUM( DECODE( t.account, '1560', 0,t.dollar_value * - 1 ) ) income, 
		    SUM( DECODE( t.account, '1560', t.dollar_value, 0 ) ) wtpaid 
		    FROM sysadmin.trx_detail t,
                sysadmin.trx_headers h 
		    WHERE
		    h.document_date >= (TO_DATE('01-JULY-11') ) 
		    AND h.document_date <= (TO_DATE('31-JULY-11'))
		    AND( NVL( h.payment_date, h.document_date ) >=( TO_DATE('01-JULY-11')) 
                AND NVL( h.payment_date, h.document_date) <= ( TO_DATE('31-JULY-11') ) ) 
		    AND h.document_type IN( 'R', 'J', 'P' ) 
                AND t.account || t.sub_account  IN
                (SELECT c.account || c.sub_account 
		    FROM chart_of_accounts c,
                    tax_chart tc 
			  WHERE tc.tax_section = 'NZI' AND tc.item_desc = 'Interest' 
			  AND tc.item_id = c.tax_item_id )
			  
		    AND h.ledger = 'TFL' 
		    AND h.ledger = t.ledger 
		    AND h.document_type = t.document_type 
		    AND h.document_number = t.document_number 
		    AND t.sub_account != 'FA'  group by 	t.institution , t.investor)t, 
       sysadmin.institutions c,
       sysadmin.tax_investor_rwt_rates i
WHERE  t.investor              = i.investor
  AND  i.asat_date                = TO_DATE('31-july-11') 
  AND  t.institution              = c.institution (+)

GROUP BY t.institution, c.name
ORDER BY 1
;

SQL> select TO_DATE('31-july-11') 
  2  from dual;
select TO_DATE('31-july-11')
               *
ERROR at line 1:
ORA-01858: a non-numeric character was found where a numeric was expected

WHERE my_character_datatype_column = 1

WHERE my_character_datatype_column = '1'

SQL> select to_date('31-july-11', 'dd-month-yy') my_date from dual;
select to_date('31-july-11', 'dd-month-yy') my_date from dual
               *
ERROR at line 1:
ORA-01843: not a valid month

SQL> select value from v$nls_parameters
  2  where parameter = 'NLS_DATE_LANGUAGE';

VALUE
---------------------------------------------
CROATIAN

SQL> select to_date('31-july-11', 'dd-month-yy', 'nls_date_language = english') my_date from dual;

MY_DATE
-------------------
31.07.2011 00:00:00