Sort the digits of a numerical string - sql

Question

I need to SORT all the digits from some string values in Postgres.
For instance, if I have two strings, e.g.
"70005" ==> "00057"
"70001" ==> "00017"
"32451" ==> "12345"
I can't cast the strings to integer or bigint due to my logic limitations. Is it possible to do this?

Answer 1

Use a recursive cte. Take the first char. if is '0' ignore it other wise go to the begining of target string.
Then use LPAD to append 0 until you get length 10.
SQL DEMO
WITH RECURSIVE cte (id, source, target) as (
SELECT 1 as id, '70001' as source , '' as target
UNION
SELECT 2 as id, '70005' as source , '' as target
UNION ALL
SELECT id,
substring(source from 2 for length(source)-1) as source,
CASE WHEN substring(source from 1 for 1) = '0' THEN target
ELSE substring(source from 1 for 1) || target
END
FROM cte
WHERE length(source) > 0
), reverse as (
SELECT id,
target,
row_number() over (partition by id
order by length(target) desc) rn
FROM cte
)
SELECT id, LPAD(target::text, 10, '0')
FROM reverse
WHERE rn = 1
OUTPUT
| id | lpad |
|----|------------|
| 1 | 0000000017 |
| 2 | 0000000057 |

Answer 2

Assuming that your data is organized like this:
Table: strings
| id | string |
|----+---------|
| 1 | '70005' |
| 2 | '70001' |
etc...
Then you can use a query like this:
SELECT all_digits.id,
array_to_string(array_agg(all_digits.digit ORDER BY all_digits.digit), '')
FROM (
SELECT strings.id, digits.digit
FROM strings, unnest(string_to_array(strings.string, NULL)) digits(digit)
) all_digits
GROUP BY all_digits.id
What this query does is split your table up into one row for each character in the string, sorts the table, and then aggregates the characters back into a string.
There's a SQL fiddle here: http://sqlfiddle.com/#!15/7f7fb0/14