Oracle 11g Release 2

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

select * from V$VERSION;


BANNER


Oracle Database 11g Express Edition Release 11.2.0.2.0 - 64bit Production

PL/SQL Release 11.2.0.2.0 - Production

CORE 11.2.0.2.0 Production

TNS for Linux: Version 11.2.0.2.0 - Production

NLSRTL Version 11.2.0.2.0 - Production


--Результат подзапроса (отфильтрованных клиентов)
create table df (idclient, idblank, dt) as
    select 1, 1, date'2021-03-01'+0.5 from dual union all  
    select 1, 2, date'2021-03-02'+0.5 from dual union all 
    select 1, 3, date'2021-03-03'+0.5 from dual union all 
    select 2, 4, date'2021-03-02'+0.5 from dual union all 
    select 2, 5, date'2021-03-03'+0.5 from dual union all 
    select 2, 6, date'2021-03-04'+0.5 from dual union all 
    select 3, 7, date'2021-03-03'+0.5 from dual union all 
    select 3, 8, date'2021-03-04'+0.5 from dual union all 
    select 3, 9, date'2021-03-05'+0.5 from dual
    
9 rows affected

select
 idclient
 ,idblank
 ,dt
from df
where dt in (
  select
  min(dt) over (partition by idclient)
  from df
  )


IDCLIENT
IDBLANK
DT


1
1
01-MAR-21

1
2
02-MAR-21

1
3
03-MAR-21

2
4
02-MAR-21

2
5
03-MAR-21

3
7
03-MAR-21

IDCLIENT	IDBLANK	DT
1	1	01-MAR-21
1	2	02-MAR-21
1	3	03-MAR-21
2	4	02-MAR-21
2	5	03-MAR-21
3	7	03-MAR-21