How to Safely Extract the nth Element from a Comma-Separated List Using REGEXP_SUBSTR and Handle Nulls?

Selecting nth Value from a List with REGEX and Null Handling

Extracting the nth element from a comma-separated list can be achieved using REGEXP_SUBSTR(), but it can fail when encountering null values. To address this issue, consider the following solution:

The regex used is (.*?)(,|$), which captures everything before the nth occurrence of a comma or the end of the line. The .*? non-greedy pattern matches the minimum number of characters necessary to reach the comma. The nth subgroup represents the value being searched.

SELECT REGEXP_SUBSTR('1,,3,4,5', '(.*?)(,|$)', 1, 2, NULL, 1) AS data
FROM dual;

-- Output: NULL

This approach ensures that null values are returned as null, regardless of their position in the list.

To enhance reusability, consider encapsulating the regex logic in a function:

FUNCTION GET_LIST_ELEMENT(string_in VARCHAR2, element_in NUMBER, delimiter_in VARCHAR2 DEFAULT ',') RETURN VARCHAR2 AS
BEGIN
  RETURN REGEXP_SUBSTR(string_in, '(.*?)(\'||delimiter_in||'|$)', 1, element_in, NULL, 1);
END GET_LIST_ELEMENT;

Using this function simplifies the extraction process:

SELECT GET_LIST_ELEMENT('123,222,,432,555', 4) AS value
FROM dual;

-- Output: 432

This approach handles null values effectively and provides a versatile solution for extracting data from comma-separated lists.

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