Return substring up to first digit

I am trying to group rows by a field that either开发者_如何学Go has the pattern [:alpha:][:digit:].* or [:alpha:][:alpha:][:digit:].* by the substring up to but excluding the digit. i.e. the returned substring will either have one letter, or two.

I am thinking something along the lines of:

SELECT
  LEFT(postcode,IF(ISDIGIT(postcode,2),1,2)) AS area,
  COUNT(*) AS num
FROM addresses
GROUP BY
  LEFT(postcode,IF(ISDIGIT(postcode,2),1,2))

Except of course there is no ISDIGIT() function.

I was also thinking of something similar to LEFT(postcode,POSITION_REGEX("\d" IN postcode)) but obviously that doesn't exist either :-/

Database server is running MySQL 4.1.24

Upgrading to 5.0 is possible but would require downtime and hasn't been done yet as it hasn't been necessary so far.

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SELECT
    LEFT(postcode, IF(postcode REGEXP '^.[[:digit:]]', 1, 2)) AS area,
    COUNT(*) AS num
FROM addresses
GROUP BY area