Ensure percentages are between 0 and 1, inclusive (using a single function)
Ok, this can't be a serious question, reminds me of https://codegolf.stackexchange.com/

I can do better, no function at all.

select
  percent_decimal,
  case
    when percent_decimal &lt;= 0 then 0
    when percent_decimal &gt;= 1 then 1
    else percent_decimal
  end as percent_modified
from condition;

PERCENT_DECIMAL PERCENT_MODIFIED
--------------- ----------------
          -0.01                0
             .1               .1
              1                1
            1.1                1


But we need a function. Finally Oracle 12.2 allows long (128 bytes) identifiers, so we can give more meaningful names:

with function 
  "Convert -0.01 to 0, Leave .1 as is, Leave 1 as is, Convert 1.1 to 1" (p number)
return number
as
begin
  if (p = -0.01) then return 0; end if;
  if (p = 1.1) then return 1; end if;
  return p;
end;
select
  percent_decimal,
  "Convert -0.01 to 0, Leave .1 as is, Leave 1 as is, Convert 1.1 to 1"(percent_decimal) 
    as percent_modified
from condition;

PERCENT_DECIMAL PERCENT_MODIFIED
--------------- ----------------
          -0.01                0
             .1               .1
              1                1
            1.1                1


I also happen to have a super secret function that coincidentally does exactly what you need:

create or replace function "." wrapped
a000000
1
abcd
abcd
abcd
abcd
abcd
abcd
abcd
abcd
abcd
abcd
abcd
abcd
abcd
abcd
abcd
8
97 aa
30RI5qP/Li6VhppxgO2AXQw62mYwg1xfrZ6pfI6iO8cYr/L9s3tguDonZ52omRm1G6sfUCen
xkcEU/4jCxrp7Ii4VNrCrVY6cDr0UNz1Id5vZ5p7e0S0F+AEd55sz9JyGokPaBbDJHFVdW+A
IAHg6Xpxmglu3BtbDtBmCA==

/



select
  percent_decimal,
  "."(percent_decimal) as percent_modified
from condition;

PERCENT_DECIMAL PERCENT_MODIFIED
--------------- ----------------
          -0.01                0
             .1               .1
              1                1
            1.1                1



Must use a built-in function? No problem.

select
  percent_decimal,
  round(percent_decimal/1.05, 1) as percent_modified
from condition;

PERCENT_DECIMAL PERCENT_MODIFIED
--------------- ----------------
          -0.01                0
             .1               .1
              1                1
            1.1                1