-- EXAMPLE
select 
    '0004V0' as TESTER_STRING
    , CHARINDEX('V','0004V0') -- OUTPUT: 5
    , CHARINDEX('0','0004V0') -- OUTPUT: 1
    , CHARINDEX('0','0004V0',4) -- OUTPUT: 6
from DUAL;

-- SYNTAX
CHARINDEX(/*substring*/, /*Main string*/, /*start index*/)