Getting an error while creating a PL/SQL function - oracle

Question

Question is : Function: Create a Function named 'find_credit_card' which takes card_no as input and returns the holder name of type varchar.
Function name: find_credit_card
Input Parameter: card_no with data type as varchar
Output variable : holder_name with data type as varchar(30)
Hint: Add '/' after the end statement
Refer to the schema.
My code :-
CREATE OR REPLACE FUNCTION find_credit_card(card_no IN VARCHAR2(255))
RETURN VARCHAR
IS
holder_name VARCHAR(255)
BEGIN
SELECT name
INTO holder_name
from credit_card
where card_number = card_no;
RETURN(holder_name);
END;
/
Warning : Function created with compilation errors.

Answer 1

Error(s) you got can be reviewed in SQL*Plus by running show err:
Warning: Function created with compilation errors.
SQL> show err
Errors for FUNCTION FIND_CREDIT_CARD:
LINE/COL ERROR
-------- -----------------------------------------------------------------
1/46 PLS-00103: Encountered the symbol "(" when expecting one of the
following:
:= . ) , # % default character
The symbol ":=" was substituted for "(" to continue.
5/1 PLS-00103: Encountered the symbol "BEGIN" when expecting one of
the following:
:= ; not null default character
SQL>
Alternatively, query user_errors:
select line, position, text
from user_errors
where name = 'FIND_CREDIT_CARD';
Oracle says that there are two errors:
first one means that function's parameter shouldn't have size, so - not card_no in varchar2(255) but only card_no in varchar2
another one means that you forgot to terminate line where local variable was declared (missing semi-colon at the end of that line):
holder_name VARCHAR(255);
However, consider inheriting datatype from column description. If it is ever changed, you wouldn't have to modify your code.
Furthermore, it would be good if you distinguish parameters and local variables from column names. How? Use prefixes, e.g. par_ for parameters, l_ or v_ for local variables.
Also, Oracle recommends us to use varchar2, not varchar.
Finally, that function might look like this:
SQL> CREATE OR REPLACE FUNCTION find_credit_card
2 (par_card_number IN credit_card.card_number%TYPE)
3 RETURN credit_card.name%type
4 IS
5 l_holder_name credit_card.name%TYPE;
6 BEGIN
7 SELECT name
8 INTO l_holder_name
9 FROM credit_card
10 WHERE card_number = par_card_number;
11
12 RETURN l_holder_name;
13 END;
14 /
Function created.
SQL> select find_credit_card('HR123456789') holder from dual;
HOLDER
---------------------------------------------------------------------
Littlefoot
SQL>