Column interquartile range and box-and-whisker plot

iqt.sql

/*
  Column interquartile range and box-and-whisker plot
  eg */ select * from _meta (
    '{app_public}',
    '{data_report_session,data_raw_session,data_report}'),
    _iqt(_schema,_relname,_column,_type);/*
*/
create function _iqt(_schema name, _relname name, _column name, _type text)
  returns table (_quartiles json, _whiskers text) as $function$
    select xmltable.* from (select query_to_xml(format(case

      when _type ~ 'int\d|float|numeric' then $$
        select 
          array_to_json(array_agg(row_to_json(r))) as _quartiles,
          repeat(' ',ceil(low/high*30)::int)
          || repeat('-',ceil((q1-low)/high*30)::int)
          || repeat('■', ceil((median-q1)/high*30)::int)
          || '|'
          || repeat('■', ceil((q3-median)/high*30)::int)
          || repeat('-', ceil((high-q3)/high*30)::int)  as _whiskers
        from (
          select 
            min(%3$I) low,
            percentile_cont(.25) within group (order by %3$I) q1,
            percentile_cont(.5) within group (order by %3$I) median,
            percentile_cont(.75) within group (order by %3$I) q3,
            max(%3$I) high
          from %1$I.%2$I) r
        group by low,q1,median,q3,high $$
      
      else 'select null'
      end,_schema,_relname,_column),false,false,'')) q,
      xmltable('//table/row' passing query_to_xml columns _quartiles json, _whiskers text)
    
$function$ language sql stable;