How to build “Star Rating” report in BigQuery (or sparklines, or color gradients)

Question

Suppose I have the followng sample input:

WITH Ratings AS (
    (SELECT \'A\' name, 2 score) UNION ALL
    (SELECT \'B\' name, 0 score) UNION ALL
    (SELECT \'C         


        

Answer 1

Fitting vertical bar chart into single character is challenging because there are only 8 different heights we could use. But horizontal bar charts don't have this limitation, we can scale horizontal chart by arbitrary length. Example below uses 30, and it shows number of births per day of week as horizontal bar chart. Data is based on public dataset:

create temp function hbar(value int64, max int64) as (
  repeat('█', cast(30 * value / max as int64))
);
select 
  ['sunday', 'monday', 'tuesday', 'wednesday',
   'thursday', 'friday', 'saturday'][ordinal(wday)] wday, bar from (
select wday, hbar(count(*), max(count(*)) over()) bar
from `bigquery-public-data.samples.natality`
where wday is not null
group by 1
order by 1 asc)

Results in

wday      bar
---------------------------------------------
sunday    ███████████████████
monday    ███████████████████████████
tuesday   ██████████████████████████████
wednesday ██████████████████████████████
thursday  █████████████████████████████
friday    █████████████████████████████
saturday  █████████████████████