extract all numbers in a string - regex

Question

How can I extract all numbers in a string?
Sample inputs:
7nr-6p
12c-18L
12nr-24L
11nr-12p
Expected Outputs:
{7,6}
{12,18}
{12,24}
etc...
The following is tested with the first one, 7nr-6p:
select regexp_split_to_array('7nr-6p', '[^0-9]') AS new_volume from mytable;
Gives: {7,"","",6,""} // Why is a numeric-only match returning spaces?
select regexp_matches('7nr-6p', '[0-9]*'::text) from mytable;
Gives: {7} // Why isn't this continuing?
select regexp_matches('7nr-6p', '\d'::text) from mytable;
Gives: {7}
select NULLIF(regexp_replace('7nr-6p', '\D',',','g'), '')::text from mytable;
Gives: 7,,,6,

Answer 1

The following query:
select regexp_split_to_array(regexp_replace('7nr-6p', '^[^0-9]*|[^0-9]*$', 'g'), '[^0-9]+')
AS new_volume from mytable;
"Trims" the prefix and suffix non-numbers and splits by the remaining non-numbers.
select regexp_matches('7nr-6p', '[0-9]*'::text) from mytable;
Gives: {7} // Why isn't this continuing?
Because without the 'g' flag, the regex stops at the first match.
Add the 'g' flag:
select regexp_matches('7nr-6p', '[0-9]*'::text, 'g') from mytable;

Answer 2

You can replace all text and then split:
SELECT regexp_split_to_array(
regexp_replace('7nr-6p', '[a-zA-Z]', '','g'),
'[^0-9]'
)
This returns {7,6}

Answer 3

SELECT id, (regexp_matches(string, '\d+', 'g'))[1]::int AS nr
FROM (
VALUES
(1, '7nr-6p')
, (2, '12c-18L')
, (3, '12nr-24L')
, (4, '11nr-12p')
) tbl(id, string);
Result:
id | nr
----+----
1 | 7
1 | 6
2 | 12
2 | 18
3 | 12
3 | 24
4 | 11
4 | 12
I wanted them in a single cell so I could extract them as needed
SELECT id, trim(regexp_replace(string, '\D+', ',', 'g'), ',') AS nrs
FROM (
VALUES
(1, '7nr-6p')
, (2, '12c-18L')
, (3, '12nr-24L')
, (4, '11nr-12p')
) tbl(id, string);
Result:
id | nrs
----+-------
1 | 7,6
2 | 12,18
3 | 12,24
4 | 11,12
dbfiddle here

Answer 4

Here is a more robust solution
CREATE OR REPLACE FUNCTION get_ints_from_text(TEXT) RETURNS int[] AS $$
select array_remove(regexp_split_to_array($1,'[^0-9]+','i'),'')::int[];
$$ LANGUAGE SQL IMMUTABLE;
Example
select get_ints_from_text('7nr-6p'); -- 7,6
-- also resilient in situations like
select get_ints_from_text('-7nr--6p'); -- 7,6
Here is a link to try
http://sqlfiddle.com/#!17/c6ac7/2
I feel that wrapping this functionality into an immutable function is prudent. This is a pure function, one that will not mutate data and one that returns the same result given the same input. Immutable functions marked as "immutable" have performance benefits.
By using a function we also benefit from abstraction. There is one source to update should this functionality need to improve in the future.
For more information about immutable functions see
https://www.postgresql.org/docs/10/static/sql-createfunction.html