Extract a number from comma separated string using regular expressions in oracle sql

Question

I am trying to fetch a number which starts with 628 in a comma separated string. Below is what I am using:

SELECT 
    REGEXP_REPLACE(REGEXP_SUBSTR('62810,5152,,', ',?628[[:alnum:]]+,?'),',','') first,
    REGEXP_REPLACE(REGEXP_SUBSTR('5152,62810,,', ',?628[[:alnum:]]+,?'),',','') second,
    REGEXP_REPLACE(REGEXP_SUBSTR('5152,562810,,', ',?628[[:alnum:]]+,?'),',','') third,
    REGEXP_REPLACE(REGEXP_SUBSTR(',5152,,62810', ',?(628[[:alnum:]]+),?'),',','') fourth
FROM DUAL;

Its working but in one case it fails which is the third column where number is 562810. Actually I am expecting NULL in the third column.

Actual output from above query is:

"FIRST","SECOND","THIRD","FOURTH"
"62810","62810","62810","62810"

Answer 1

Not sure why you are using [[:alnum::]] . You could use matching group to extract the number starting with 628 or followed by a comma. REPLACE may be avoided this way

If you have alphabets as well, modify the 2nd match group () accordingly.

SELECT 
    REGEXP_SUBSTR('62810,5152,,' , '(^|,)(628\d*)',1,1,NULL,2) first,
    REGEXP_SUBSTR('5152,62810,,' , '(^|,)(628\d*)',1,1,NULL,2) second,
    REGEXP_SUBSTR('5152,562810,,', '(^|,)(628\d*)',1,1,NULL,2) third,
    REGEXP_SUBSTR(',5152,,62810' , '(^|,)(628\d*)',1,1,NULL,2) fourth
FROM DUAL;

Demo

Answer 2

The problem with your regex logic is that you are searching for an optional comma before the numbers 628 . This means that any number having 628 anywhere would match. Instead, you can phrase this by looking for 628 which is either preceded by either a comma, or the start of the string.

SELECT
    REGEXP_REPLACE(REGEXP_SUBSTR('62810,5152,,', '(,|^)628[[:alnum:]]+,?'),',','') first,
    REGEXP_REPLACE(REGEXP_SUBSTR('5152,62810,,', '(,|^)628[[:alnum:]]+,?'),',','') second,
    REGEXP_REPLACE(REGEXP_SUBSTR('5152,562810,,', '(,|^)628[[:alnum:]]+,?'),',','') third,
    REGEXP_REPLACE(REGEXP_SUBSTR(',5152,,62810', '(,|^)(628[[:alnum:]]+),?'),',','') fourth
FROM DUAL

Demo

The ideal pattern we'd like to use here is \\b628.* , or something along these lines. But Oracle's regex functions do not appear to support word boundaries, hence we can use (^|,)628.* as an alternative.