REGEXP_SUBSTR for comma delimited list with null values

Question

Hi,
I have a column which stores a comma delimited list of values. Some of these values in the list may be null. I'm having some issues trying to extract the values using the REGEXP_SUBSTR function when null values are present. Here are two things that I've tried:
SELECT
   REGEXP_SUBSTR (val, '[^,]*', 1, 1) pos1
  ,REGEXP_SUBSTR (val, '[^,]*', 1, 2) pos2
  ,REGEXP_SUBSTR (val, '[^,]*', 1, 3) pos3
  ,REGEXP_SUBSTR (val, '[^,]*', 1, 4) pos4
  ,REGEXP_SUBSTR (val, '[^,]*', 1, 5) pos5
FROM (SELECT 'AAA,BBB,,DDD,,FFF' val FROM dual);
POS P POS P P
AAA   BBB
SELECT
   REGEXP_SUBSTR (val, '[^,]+', 1, 1) pos1
  ,REGEXP_SUBSTR (val, '[^,]+', 1, 2) pos2
  ,REGEXP_SUBSTR (val, '[^,]+', 1, 3) pos3
  ,REGEXP_SUBSTR (val, '[^,]+', 1, 4) pos4
  ,REGEXP_SUBSTR (val, '[^,]+', 1, 5) pos5
FROM (SELECT 'AAA,BBB,,DDD,,FFF' val FROM dual);
POS POS POS POS P
AAA BBB DDD FFFAs you can see neither of the calls works correctly. Does anyone know how to modify the regular expression pattern to handle null values? I've tried various other patterns but was unable to get anyone to work for all cases.
Thanks,
Martin
http://www.ClariFit.com
http://www.TalkApex.com

Answer 1

Hi, Martin,
This does what you want:
SELECT
   RTRIM (REGEXP_SUBSTR (val, '[^,]*,', 1, 1), ',') pos1
  ,RTRIM (REGEXP_SUBSTR (val, '[^,]*,', 1, 2), ',') pos2
  ,RTRIM (REGEXP_SUBSTR (val, '[^,]*,', 1, 3), ',') pos3
  ,RTRIM (REGEXP_SUBSTR (val, '[^,]*,', 1, 4), ',') pos4
  ,RTRIM (REGEXP_SUBSTR (val || ','
                      , '[^,]*,', 1, 5), ',') pos5
FROM (SELECT 'AAA,BBB,,DDD,,FFF' val FROM dual);The query above works in Oracle 10 or 11, but in Oracle 11, you can also do it with just REGEXP_SUBSTR, without using RTRIM:
SELECT
   REGEXP_SUBSTR (val, '([^,]*),|$', 1, 1, NULL, 1) pos1
  ,REGEXP_SUBSTR (val, '([^,]*),|$', 1, 2, NULL, 1) pos2
  ,REGEXP_SUBSTR (val, '([^,]*),|$', 1, 3, NULL, 1) pos3
  ,REGEXP_SUBSTR (val, '([^,]*),|$', 1, 4, NULL, 1) pos4
  ,REGEXP_SUBSTR (val, '([^,]*),|$', 1, 5, NULL, 1) pos5
FROM (SELECT 'AAA,BBB,,DDD,,FFF' val FROM dual);The problem with your first query was that it was looking for sub-strings of 0 or more non-commas. There was such as sub-string. consisting of 3 characters, starting at position 1, so it returned 'AAA', as expected. Then there was another sub-string, of 0 characters, starting at position 4, so it returned NULL. Then there was a sub-string of 3 characters starting at position 5, so it returned 'BBB'.
The problem with your 2nd query was that it was looking for 1 or more non-commas. 'DDD' is the 3rd such sub-string.
Edited by: Frank Kulash on Feb 16, 2012 11:36 AM
Added Oracle 11 example