select a,b from table(multiset{row(1,2)}) as t1(a,b)
Union 
select a, null as b from table(multiset{row(1)}) as t1(a);

201: A syntax error has occurred.
Error in line 3
Near character position 15

select a,b from table(multiset{row(1,2)}) as t1(a,b)
Union 
select a,decode(1,2,3) from table(multiset{row(1)}) as t1(a);> > 

          a           b 

          1            
          1           2

2 row(s) retrieved.

select 'Sergey' a, to_date('01.01.2011','%d.%m.%Y') b, to_date('12.01.2011','%d.%m.%Y') c from table(set{ 1 })
union all
select 'Sergey', to_date('12.01.2011','%d.%m.%Y') , to_date('31.01.2011','%d.%m.%Y') from table(set{ 1 })
union all
select 'Alla',   to_date('01.01.2011','%d.%m.%Y'), to_date('12.01.2011','%d.%m.%Y') from table(set{ 1 })
union all
select 'Alla',   to_date('01.02.2011','%d.%m.%Y'), to_date('15.02.2011','%d.%m.%Y') from table(set{ 1 })
into temp t


select distinct t.a, 
     (select min(t2.b) from t t2 where t2.a = t.a and t2.b <= t.c and t2.c >=t.b) ma,
     (select max(t2.c) from t t2 where t2.a = t.a and t2.b <= t.c and t2.c >=t.b) mb
from t