Column histogram

histogram.sql

/*
  Column histogram
  eg */ select * from _meta (
    '{app_public}',
    '{data_report_session,data_raw_session,data_report}'),
    _histogram(_schema,_relname,_column,_type);/*
*/
create function _histogram(_schema name,_relname name,_column name,_type text)
  returns setof json as $function$ begin
    return query execute format(case
      when _type ~ 'int\d|float|numeric' then $$
      select array_to_json(array_agg(row_to_json(b))) as _buckets
      from (
        select
          width_bucket(%3$I,min,max,num_buckets) bucket,
          count(*) freq,
          trunc(count(*)::numeric/"N",3) p,
          floor(100*count(*)::numeric/"N") "%%",
          trunc(min(%3$I)::numeric,3) low,
          trunc(max(%3$I)::numeric,3) high
        from %1$I.%2$I,
          (select count(*) "N", min(%3$I), max(%3$I) from %1$I.%2$I) s,
          (select (case when count(*) >= 15 then 1+3.3*log(count(*))
                 else (max(%3$I)-min(%3$I))/(2* ||/count(*) * (
                   percentile_disc(.75) within group (order by %3$I)
                   - percentile_disc(.25) within group (order by %3$I)
                 )) end)::int as num_buckets from %1$I.%2$I) nb
          
        group by bucket,"N" order by bucket
      ) b $$
    else $$ select null::json $$
    end,_schema,_relname,_column,_type);
end $function$ language plpgsql stable;