Oracle 18c

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select * from V$VERSION;


BANNER
BANNER_FULL
BANNER_LEGACY
CON_ID


Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production
Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production
Version 18.4.0.0.0
Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production
0


create table t (dat, num) as 
    select date'2015-02-23', -11800.93 from dual union all
    select date'2015-02-24', -11213.99 from dual union all
    select date'2015-02-25',         0 from dual union all
    select date'2015-06-18', -58832.61 from dual union all
    select date'2015-06-19',         0 from dual union all
    select date'2015-06-20',         0 from dual union all
    select date'2015-08-18',  -55404.6 from dual union all
    select date'2015-08-19',         0 from dual;
8 rows affected

alter session set nls_date_format='yyyy-mm-dd'
select dat old, num, 
    last_value (case when num != 0 then dat end ignore nulls) over (order by dat) new
from t


OLD
NUM
NEW


2015-02-23
-11800.93
2015-02-23

2015-02-24
-11213.99
2015-02-24

2015-02-25
0
2015-02-24

2015-06-18
-58832.61
2015-06-18

2015-06-19
0
2015-06-18

2015-06-20
0
2015-06-18

2015-08-18
-55404.6
2015-08-18

2015-08-19
0
2015-08-18

OLD	NUM	NEW
2015-02-23	-11800.93	2015-02-23
2015-02-24	-11213.99	2015-02-24
2015-02-25	0	2015-02-24
2015-06-18	-58832.61	2015-06-18
2015-06-19	0	2015-06-18
2015-06-20	0	2015-06-18
2015-08-18	-55404.6	2015-08-18
2015-08-19	0	2015-08-18