Re: Cool hack with recursive queries

Gregory Stark wrote:

> WITH RECURSIVE Z(IX, IY, CX, CY, X, Y, I) AS (
>                 SELECT IX, IY, X::float, Y::float, X::float, Y::float, 0
>                 FROM (select -2.2 + 0.031 * i, i from generate_series(0,101) as i) as xgen(x,ix),
>                      (select -1.5 + 0.031 * i, i from generate_series(0,101) as i) as ygen(y,iy)
>                 UNION ALL
>                 SELECT IX, IY, CX, CY, X * X - Y * Y + CX AS X, Y * X * 2 + CY, I + 1
>                 FROM Z
>                 WHERE X * X + Y * Y < 16::float
>                 AND I < 100
>           )
>     SELECT array_to_string(array_agg(SUBSTRING(' .,,,-----++++%%%%@@@@#### ', LEAST(GREATEST(I,1),27), 1)),'')
>     FROM (
>           SELECT IX, IY, MAX(I) AS I
>           FROM Z
>           GROUP BY IY, IX
>           ORDER BY IY, IX
>          ) AS ZT
>     GROUP BY IY
>     ORDER BY IY

FWIW you can halve the running time by restricting I to 27 instead of
100 in the recursive term, and obtain the same result.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.