Mandelbrot set in Postgres SQL

mandelbrot.sql

WITH RECURSIVE
  xaxis(x) AS (
    SELECT -2.0
    UNION ALL
    SELECT x + 0.05 FROM xaxis WHERE x < 1.2
  ),
  yaxis(y) AS (
    SELECT -1.0
    UNION ALL
    SELECT y + 0.1 FROM yaxis WHERE y < 1.0
  ),
  m(iter, cx, cy, x, y) AS (
    SELECT 0, x, y, 0.0::float, 0.0::float 
    FROM xaxis, yaxis
    UNION ALL
    SELECT iter+1, cx, cy, 
           x*x - y*y + cx, 
           2.0*x*y + cy 
    FROM m 
    WHERE (x*x + y*y) < 4.0 AND iter < 28
  ),
  m2(iter, cx, cy) AS (
    SELECT max(iter), cx, cy FROM m GROUP BY cx, cy
  ),
  mandel(line) AS (
    SELECT string_agg(
      CASE 
        WHEN iter < 7 THEN ' '
        WHEN iter < 14 THEN '.'
        WHEN iter < 21 THEN '+'
        WHEN iter < 28 THEN '*'
        ELSE '#'
      END,
      '' ORDER BY cx
    ) as line
    FROM m2 
    GROUP BY cy
    ORDER BY cy DESC
  )
SELECT line FROM mandel;