How do I split text into multiple fields using Postgresql? - postgresql

Question

I have a table with a column that needs to be split and inserted into a new table. Column's name is location and has data that could look like Detroit, MI, USA;Chicago, IL, USA or as simple as USA.
Ultimately, I want to insert the data into a new dimension table that looks like:
City | State | Country|
Detroit MI USA
Chicago IL USA
NULL NULL USA
I came across the string_to_array function and am able to split the larger example (Detroit, MI, USA; Chicago, IL, USA) into 2 strings of Detroit, MI, USA and Chicago, IL, USA.
Now I'm stumped on how to split those strings again and then insert them. Since there are two strings separated by a comma, does using string_to_array again work? It doesn't seem to work in Sqlfiddle.
Note: I'm using Sqlfiddle right now since I don't have access to my Redshift table at the moment.
This is for Redshift, which unfortunately is still using PostGresql 8.0.2 and thus does not have the unnest function

Answer 1

postgres=# select v[1] as city, v[1] as state, v[2] as country
from (select string_to_array(unnest(string_to_array(
'Detroit, MI, USA;Chicago, IL, USA',';')),',')) s(v);
┌─────────┬─────────┬─────────┐
│ city │ state │ country │
╞═════════╪═════════╪═════════╡
│ Detroit │ Detroit │ MI │
│ Chicago │ Chicago │ IL │
└─────────┴─────────┴─────────┘
(2 rows)
Tested on Postgres, not sure if it will work on Redshift too
Next query should to work on every Postgres
select v[1] as city, v[1] as state, v[2] as country
from (select string_to_array(v, ',') v
from unnest(string_to_array(
'Detroit, MI, USA;Chicago, IL, USA',';')) g(v)) s;
It use old PostgreSQL trick - using derived table.
SELECT v[1], v[2] FROM (SELECT string_to_array('1,2',',')) g(v)
Unnest function:
CREATE OR REPLACE FUNCTION _unnest(anyarray)
RETURNS SETOF anyelement AS '
BEGIN
FOR i IN array_lower($1,1) .. array_upper($1,1) LOOP
RETURN NEXT $1[i];
END LOOP;
RETURN;
END;
' LANGUAGE plpgsql;