Search notes:

Oracle SQL function: SUBSTR

substr has to mandatory and one optional parameter:

substr( text , position )
substr( text , position , length )

Two parameters

With two parameters, substr returns the portion of text from character position through the end of text.

select
   substr(
      '1234567890', -- Text
       5            -- Start position
   )
from
   dual;
--
-- 567890

The optional third parameter is used to limit the length of the returned string:

select
   substr(
      '1234567890', -- Text
       5          , -- Start position
       3            -- Length
   )
from
   dual;
--
-- 567

substr comes in five variants: