Question

can you help me to split a string (or preferred if possible, place a blank at every “split” occasion) after every change from alphanumeric to numeric and vice versa ?

So a string like D2c1 22 should look like D 2 c 1 22. Best way from would be to put a blank at every change from alpha-numeric to numeric.

Answer 1

Here’s an approach tested with PostgreSQL and verified to work. It’s a bit tortured, so performance might be … interesting.

CREATE AGGREGATE array_cat_agg (
  BASETYPE = anyarray,
  SFUNC = array_cat,
  STYPE = anyarray
);
SELECT array_to_string(array_cat_agg(a), ' ')
FROM regexp_matches('234kjh23ljkgh34klj2345klj', '(\D*)(\d*)', 'g') x(a);

We need array_cat_agg because regular array_agg can’t aggregate arrays of arrays.

Alternately, a form of @davidrac’s approach that’ll work with PostgreSQL and probably perform significantly better (though I haven’t tested) is:

SELECT regexp_replace(
  regexp_replace(
     '234kjh23ljkgh34klj2345klj', '(\d)(\D)', '\1 \2', 'g'
  ), '(\D)(\d)', '\1 \2', 'g');

This is executing the replacement in two passes. First it’s inserting a space where series of digits end and series of non-digits begin. Then in another pass it’s inserting spaces where series of non-digits end and series of digits begin.

Update: Here’s an improved formulation:

SELECT trim(regexp_replace('234kjh23ljkgh34klj2345klj', '(?!\d)(\D+)|(?!\D)(\d+)', '\1\2 ', 'g'));