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       ★☆☆☆☆