SELECT substr('test',0,0) as sub1 ,
       substr('test',0,-1) as sub2,
       substr('test',0,2) as sub3,
       substr('test',1,1) as sub4,
       substr('test',1,2) as sub5,
       substr('test',1,4) as sub6,
       substr('test',1,5) as sub7,
       substr('test',2) as sub8,
       substr('test',5) as sub9
from dual;


sub1 sub2 sub3 sub4 sub5 sub6 sub7 sub8 sub9
---- ---- ---- ---- ---- ---- ---- ---- ----
null null   te    t   te test test  est	null