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

We can build star rating as a string using two Unicode characters:

★ - Unicode code point 9733 
☆ - Unicode code point 9734

We can use CODE_POINTS_TO_STRING function to build the stars, and REPEAT function to produce the right number of stars

Combined together the solution for sample input will be:

WITH Ratings AS (
(SELECT 'A' name, 2 score) UNION ALL
(SELECT 'B' name, 0 score) UNION ALL
(SELECT 'C' name, 5 score) UNION ALL
(SELECT 'D' name, 1 score))

SELECT 
  name, 
  CONCAT(
    REPEAT(CODE_POINTS_TO_STRING([9733]), score),
    REPEAT(CODE_POINTS_TO_STRING([9734]), 5-score)) score
FROM Ratings

It will produce the following result:

name    score
A       ★★☆☆☆
B       ☆☆☆☆☆
C       ★★★★★
D       ★☆☆☆☆

Answer 2

Adding more-less generic option for producing time-series/sparklines type of report

#standardSQL
CREATE TEMP FUNCTION sparklines(arr ARRAY<INT64>) AS ((
  SELECT STRING_AGG(CODE_POINTS_TO_STRING([code]), '') 
  FROM UNNEST(arr) el, 
  UNNEST([(SELECT MAX(el) FROM UNNEST(arr) el)]) mx, 
  UNNEST([(SELECT MIN(el) FROM UNNEST(arr) el)]) mn
  JOIN UNNEST([9602, 9603, 9605, 9606, 9607]) code WITH OFFSET pos
  ON pos = CAST(IF(mx = mn, 1, (el - mn) / (mx - mn)) * 4 AS INT64) 
)); 
WITH series AS (
  SELECT 1 id, [3453564, 5343333, 2876345, 3465234] arr UNION ALL
  SELECT 2, [5743231, 3276438, 1645738, 2453657] UNION ALL
  SELECT 3, [1,2,3,4,5,6,7,8,9,0] UNION ALL
  SELECT 4, [3245876, 2342879, 5876324, 7342564]  
)  
SELECT 
  id, TO_JSON_STRING(arr) arr, sparklines(arr) sparklines 
FROM series 

with result as below

Row id  arr                                 sparklines   
1   1   [3453564,5343333,2876345,3465234]   ▃▇▂▃     
2   2   [5743231,3276438,1645738,2453657]   ▇▅▂▃     
3   3   [1,2,3,4,5,6,7,8,9,0]               ▂▃▃▅▅▆▆▇▇▂   
4   4   [3245876,2342879,5876324,7342564]   ▃▂▆▇       

Adding Mosha's version (taken from his comments below)

#standardSQL
CREATE TEMP FUNCTION barchart(v ARRAY<FLOAT64>, MIN FLOAT64, MAX FLOAT64) AS ( 
  IF(
    MIN = MAX, 
    REPEAT(CODE_POINTS_TO_STRING([9603]), ARRAY_LENGTH(v)), 
    (
    SELECT STRING_AGG(CODE_POINTS_TO_STRING([9601 + CAST(ROUND(y) AS INT64)]), '') 
    FROM ( 
      SELECT SAFE_DIVIDE(e-min, MAX - MIN) * 7 y 
      FROM UNNEST(v) e)
    )
  )
); 
CREATE TEMP FUNCTION vbar(v ARRAY<FLOAT64>) AS ( 
  barchart(v, (SELECT MIN(a) FROM UNNEST(v) a), (SELECT MAX(a) FROM UNNEST(v) a)) 
);
WITH numbers AS (
  SELECT 1 id, [3453564., 5343333., 2876345., 3465234.] arr UNION ALL
  SELECT 2, [5743231., 3276438., 1645738., 2453657.] UNION ALL
  SELECT 3, [1.,2,3,4,5,6,7,8,9,0] UNION ALL
  SELECT 4, [3245876., 2342879, 5876324, 7342564]  
)  
SELECT 
  id, TO_JSON_STRING(arr) arr, vbar(arr) sparklines 
FROM numbers  

if applied to same dummy data as above versions - produces below

Row id  arr                                 sparklines   
1   1   [3453564,5343333,2876345,3465234]   ▃█▁▃     
2   2   [5743231,3276438,1645738,2453657]   █▄▁▂     
3   3   [1,2,3,4,5,6,7,8,9,0]               ▂▃▃▄▅▆▆▇█▁   
4   4   [3245876,2342879,5876324,7342564]   ▂▁▆█      

Answer 3

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  █████████████████████

Answer 4

More craziness here

Answer 5

My entry does a color gradient, because sparklines only look good with certain fonts - and that's not a font that the BigQuery web UI uses.

During a day, when is Stack Overflow the most active per tag:

#standardSQL
CREATE TEMP FUNCTION barchart(v ARRAY<FLOAT64>, mm STRUCT<min FLOAT64, max FLOAT64>) AS ((
    SELECT STRING_AGG(SUBSTR('