Counting with letters instead of numbers

Question

hi everybody,
today I got the requirement to represent the rownums of a recordset (1, 2, 3, 4, 5 and so on) as letters (A, B, C, D, E and so on). First of all I thought there is a database function equal to the to_char function with RN parameter (which is able to convert numbers to roman numbers easily)... but I didn´t find anything.
So, is there a database function that I haven´t found yet or have you got some custom code for me to realize this?
ty in advance
- Oliver

Answer 1

Hi,
I don't think it's quite that simple. OP does not want a base-26 number, because there is nothing quite like a 0 in this system, and therefore nothing quite like a leading 0.
In a base-26 system, you could represent 26 ^2^ distinct numbers with strings up to 2 characters.
OP wants something where you can represent 26 ^2^ + 26 distinct numbers with strings up to 2 characters: 26 numbers with 1-character strings and a completely disjoint set of 26 ^2^ numbers with 2-character strings.
I think OP needs something more complicated, like this:
CREATE OR REPLACE FUNCTION to_abc
(      in_num       IN        PLS_INTEGER               -- Number to be converted
RETURN     VARCHAR2
DETERMINISTIC
IS
     in_num_26     PLS_INTEGER    := MOD (in_num, 26);
     rest          PLS_INTEGER;
     return_txt     VARCHAR2 (30);
BEGIN
     IF  in_num IS NULL
     THEN
          RETURN     NULL;
     ELSIF  in_num <= 0
     THEN
          RETURN  '-';
     END IF;
     return_txt := CHR ( 64 + CASE
                         WHEN  in_num_26 = 0
                         THEN  26
                         ELSE  in_num_26
                              END
     rest := CEIL (in_num / 26);
     IF  rest = 1
     THEN
          RETURN     return_txt;
     ELSE
          RETURN  to_abc (rest - 1) || return_txt;
     END IF;
END     to_abc;Test script (including your base26 function, for comparison):
COLUMN     base26          FORMAT     A10
COLUMN     right_txt     FORMAT     A10
COLUMN     to_abc          FORMAT     A10
SET     NULL     "[NULL]"
WITH test_nums     AS
     SELECT     0 AS n,     '-' AS right_txt     FROM dual     UNION ALL
     SELECT     1,        'A'               FROM dual     UNION ALL
     SELECT     10,        'J'               FROM dual     UNION ALL
     SELECT     26,        'Z'               FROM dual     UNION ALL
     SELECT     27,        'AA'               FROM dual     UNION ALL
     SELECT     28,        'AB'               FROM dual     UNION ALL
     SELECT     52,        'AZ'               FROM dual     UNION ALL
     SELECT     53,        'BA'               FROM dual     UNION ALL
     SELECT     78,        'BZ'               FROM dual     UNION ALL
     SELECT     79,        'CA'               FROM dual     UNION ALL
     SELECT     702,        'ZZ'               FROM dual     UNION ALL
     SELECT     703,        'AAA'               FROM dual     UNION ALL
     SELECT     1404,       'BAZ'               FROM dual     UNION ALL
     SELECT     1405,       'BBA'               FROM dual     UNION ALL
     SELECT     18278,     'ZZZ'               FROM dual     UNION ALL
     SELECT     18279,     'AAAA'               FROM dual     UNION ALL
     SELECT     18280,     'AAAB'               FROM dual     UNION ALL
     SELECT     NULL,     NULL               FROM dual
SELECT     n
,     to_abc (n)     AS to_abc
,     right_txt
,     CASE
          WHEN  NVL (to_abc (n), '??') =
                NVL (right_txt,  '??')
          THEN  ' '
          ELSE  '<== WRONG!'
     END             AS flag
,     base26 (n)     AS base26
FROM     test_nums
ORDER BY  n
;Results of test script:
.        N TO_ABC     RIGHT_TXT  FLAG       BASE26
         0 -          -                     [NULL]
         1 A          A                     a
        10 J          J                     j
        26 Z          Z                     aa
        27 AA         AA                    aa
        28 AB         AB                    ab
        52 AZ         AZ                    ba
        53 BA         BA                    ba
        78 BZ         BZ                    ca
        79 CA         CA                    ca
       702 ZZ         ZZ                    aaa
       703 AAA        AAA                   aaa
      1404 BAZ        BAZ                   bba
      1405 BBA        BBA                   bba
     18278 ZZZ        ZZZ                   aaaa
     18279 AAAA       AAAA                  aaaa
     18280 AAAB       AAAB                  aaab
[NULL]     [NULL]     [NULL]                [NULL]