circle.sql

with recursive
limitxy AS (SELECT * FROM (VALUES(20, 20)) AS t (x,y)),
formula(n, x, y, c) AS (
        VALUES(0, 0, 0, '')
        UNION ALL
        SELECT n+1,
            (SELECT x FROM (SELECT n % (SELECT x FROM limitxy) AS x, n / (SELECT x FROM limitxy) AS y) AS xy),
            (SELECT y FROM (SELECT n % (SELECT x FROM limitxy) AS x, n / (SELECT x FROM limitxy) AS y) AS xy),
            CASE WHEN (
                SELECT (abs(point.x * point.x + point.y * point.y - 80) < 8)　　　　-- 条件式
                FROM (
                    SELECT x - (SELECT x/2 FROM limitxy) AS x, y - (SELECT y/2 FROM limitxy) AS y
                    FROM (SELECT n % (SELECT x FROM limitxy) AS x, n / (SELECT y FROM limitxy) AS y) AS xy
                    ) AS point
                )
            then '*'
            ELSE ' '
            END
        FROM formula WHERE n < (SELECT x * y FROM limitxy)
    ),
mkstring(num, s) AS(
    VALUES(0, '')
    UNION ALL
    SELECT num + 1, (SELECT ARRAY_TO_STRING(ARRAY_AGG(c), '') FROM formula WHERE num = formula.y) FROM mkstring WHERE num < (SELECT y FROM limitxy)
)
SELECT s FROM mkstring WHERE num != 0;
          s
----------------------

         *****
       **     **
     **         **
    *             *
    *             *
   *               *
   *               *
  *                 *
  *                 *
  *                 *
  *                 *
  *                 *
   *               *
   *               *
    *             *
    *             *
     **         **
       **     **
         *****
(20 rows)