Loop through slices of 2-dimensional array in plpgsql function? How to loop through an array of arrays in a function and access its elements?

Below is the the function (this is only the relevant part).

create  or replace function public.whatwhatwhy(
        _fields character varying []
    ) returns void as 
$func$
declare strSQL text := '';
declare _field text := '';
begin 
    foreach _field in array _fields[:][1:2]
        loop 
            strSQL :=  'fieldname:' || _field[1] || ' stats: ' || _field[2] ;
            raise notice '% EXECUTING %', to_char(now(), 'YYYY-MM-DD HH24:MI:SS'), strSQL;
        end loop;
end
$func$ language plpgsql;


I want to call the function with: 

select public.whatwhatwhy(ARRAY[
['total_pop', 'sum'],
['total_male_pop','sum'],
['median_female_age','median']
])


Question
How do I access e.g. total_pop and sum in my _field? I assumed the _field variable holds another array however I get an error:


  SQL Error [42804]: ERROR: cannot subscript type text because it is not an array
  Where: SQL statement "SELECT 'fieldname:' || _field[1] || ' stats: ' || _field[2]"


Note

I tried this statement, hoping that this solves the problem, but it seems to be identical to the statement above.  

select public.whatwhatwhy(ARRAY[
ARRAY['total_pop', 'sum'],
ARRAY['total_male_pop','sum'],
ARRAY['median_female_age','median']
])
A FOR loop over array_upper(_fields,1) like you found is a simple and good option.

Even simpler for your case (for Postgres 9.1 or later): FOREACH with SLICE. The manual:


  With a positive SLICE value, FOREACH iterates through slices of the
  array rather than single elements.


Your function could look like this:

CREATE OR REPLACE FUNCTION public.mj_rubbish(_fields text[])
   RETURNS void AS
$func$
DECLARE
   m text[];
BEGIN
   FOREACH m SLICE 1 IN ARRAY _fields
   LOOP
      RAISE NOTICE '% EXECUTING fieldname: %, stats: %', now()::text, m[1], m[2];
   END LOOP;
END
$func$  LANGUAGE plpgsql;


This also works regardless of actual array indices - which do no have to start with 1 (but do by default).

Related:


Loop over array dimension in plpgsql
Step through multiple arrays in parallel with FOREACH
Normalize array subscripts for 1-dimensional array so they start with 1