Home >Database >Mysql Tutorial >SQL也疯狂：MySQL绘制简单几何图形(2013-04-12)

SQL也疯狂：MySQL绘制简单几何图形(2013-04-12)

WBOYOriginal: 2016-06-07 14:57:001488browse

用SQL SELECT 语句而非存储过程来画基本几何图形，以加深对 SELECT 语句的理解。因为 SELECT 语句隐含了一个或多个循环，看上去只是一个语句，其实包含了一个完整的程序所包含的顺序、分支、循环，因此不必用存储过程就能实现一般的程序的功能需要有一个表

用SQL SELECT 语句而非存储过程来画基本几何图形，以加深对 SELECT 语句的理解。因为 SELECT 语句隐含了一个或多个循环，看上去只是一个语句，其实包含了一个完整的程序所包含的顺序、分支、循环，因此不必用存储过程就能实现一般的程序的功能

需要有一个表有 100 行以上的数据，数据是什么没关系，因为下面的语句已经避开使用数据库记录中的数据了。如果没有现成的就使用如下代码生成一个吧：语句

DELIMITER ;;

DROP PROCEDURE IF EXISTS test_num;;

CREATE PROCEDURE test_num(MAX_COUNT INTEGER)
BEGIN
	DECLARE i INTEGER;
	SET i = 0;

	DROP TABLE IF EXISTS number;
	CREATE TABLE number(num INT(10), PRIMARY KEY (num));

	WHILE i < MAX_COUNT DO
		INSERT INTO number(num) VALUES (i);
		SET i = i + 1;
	END WHILE;
END;;

DELIMITER ;

CALL test_num(100);

画横线语句

SET @w := 24;  # 宽 <span>SELECT</span> repeat(<span>"*"</span>, @w) AS line;

结果

+--------------------------+
| line                     |
+--------------------------+
| ************************ |
+--------------------------+

画竖线语句

SET @h := 12;  # 高
SET @y := 0;   # y 座标 <span>SELECT</span> <span>"*"</span> AS line <span>FROM</span> number <span>WHERE</span> @y < @h and @y := @y + 1;

结果

+------+
| line |
+------+
| *    |
| *    |
| *    |
| *    |
| *    |
| *    |
| *    |
| *    |
| *    |
| *    |
| *    |
| *    |
+------+

画斜线语句

SET @h := 12;   # 高
SET @y := 0;    # y 座标
SET @rate := 2; # x y 座标比例（斜率倒数） <span>SELECT</span> lpad(<span>"*"</span>, @y * @rate, <span>" "</span>) AS line <span>FROM</span> number <span>WHERE</span> @y < @h and @y := @y + 1;

结果

+--------------------------+
| line                     |
+--------------------------+
|  *                       |
|    *                     |
|      *                   |
|        *                 |
|          *               |
|            *             |
|              *           |
|                *         |
|                  *       |
|                    *     |
|                      *   |
|                        * |
+--------------------------+

画XX 语句

SET @h := 12;           # 高
SET @w := 24;           # 宽
SET @y := 0;            # y 座标
SET @rate := @w / @h;   # x y 座标比例（斜率倒数） <span> SELECT</span> X <span>FROM</span> ( <span> SELECT</span> concat(lpad(<span>"*"</span>, @y * @rate - 1, <span>" "</span>), repeat(<span>" "</span>, @w - 2 * @y * @rate - 2 + 1), IF(@w - 2 * @y * @rate - 2 + 1 <= 0, <span>"",  "</span>*")) AS X <span>FROM</span> number <span>WHERE</span> @y < @h / 2 and @y := @y + 1

    UNION ALL <span> SELECT</span> concat(lpad(<span>"*"</span>, @y * @rate - 1, <span>" "</span>), repeat(<span>" "</span>, @w - 2 * @y * @rate - 2 + 1), IF(@w - 2 * @y * @rate - 2 + 1 <= 0, <span>"",  "</span>*")) AS X <span>FROM</span> number <span>WHERE</span> @y < @h and (@y := @y - 1) > 0
) AS Temp;

结果

+-----------------------+
| X                     |
+-----------------------+
| *                   * |
|   *               *   |
|     *           *     |
|       *       *       |
|         *   *         |
|           *           |
|         *   *         |
|       *       *       |
|     *           *     |
|   *               *   |
| *                   * |
+-----------------------+

画矩形语句

SET @x := 0;    # x 座标
SET @rate := 2; # x y 轴长比例，调整显示效果
SET @h := 12;   # 长
SET @w := 12;   # 宽 <span> SELECT</span> rect <span>FROM</span> ( <span>SELECT</span> repeat(<span>"*"</span>, @w * @rate) AS rect 

    UNION ALL <span> SELECT</span> concat(<span>"*"</span>, repeat(<span>" "</span>, @w * @rate - 2), <span>"*"</span>) <span>FROM</span> number <span>WHERE</span> @x < @h and @x := @x + 1

    UNION ALL <span>SELECT</span> repeat(<span>"*"</span>, @w * @rate)
) AS Temp;

结果

+--------------------------+
| rect                     |
+--------------------------+
| ************************ |
| *                      * |
| *                      * |
| *                      * |
| *                      * |
| *                      * |
| *                      * |
| *                      * |
| *                      * |
| *                      * |
| *                      * |
| *                      * |
| *                      * |
| ************************ |
+--------------------------+

把XX用矩形框起来语句

SET @h := 12;           # 高
SET @w := 24;           # 宽
SET @y := 0;            # y 座标
SET @rate := @w / @h;   # x y 座标比例（斜率倒数） <span> SELECT</span> rectXX <span>FROM</span> ( <span>SELECT</span> repeat(<span>"*"</span>, (@w - 2 * 2)) AS rectXX

    UNION ALL <span>SELECT</span> concat(<span>"*"</span>, lpad(<span>"*"</span>, @y * @rate - 1, <span>" "</span>), repeat(<span>" "</span>, (@w - 2 * 2) - 2 * @y * @rate - 2 + 1), IF((@w - 2 * 2) - 2 * @y * @rate - 2 + 1 <= 0, <span>"",  "</span>*<span>"), repeat("</span> <span>", @y * @rate - 1), "</span>*") <span>FROM</span> number <span>WHERE</span> @y < (@h - 2) / 2 and @y := @y + 1

    UNION ALL <span> SELECT</span> concat(<span>"*"</span>, lpad(<span>"*"</span>, @y * @rate - 1, <span>" "</span>), repeat(<span>" "</span>, (@w - 2 * 2) - 2 * @y * @rate - 2 + 1), IF((@w - 2 * 2) - 2 * @y * @rate - 2 + 1 <= 0, <span>"",  "</span>*<span>"), repeat("</span> <span>", @y * @rate - 1), "</span>*") <span>FROM</span> number <span>WHERE</span> @y < (@h - 2) and (@y := @y - 1) > 0

    UNION ALL <span>SELECT</span> repeat(<span>"*"</span>, (@w - 2 * 2)) AS rect
) AS Temp;

结果

+----------------------+
| rectXX               |
+----------------------+
| ******************** |
| **               * * |
| *  *           *   * |
| *    *       *     * |
| *      *   *       * |
| *        *         * |
| *      *   *       * |
| *    *       *     * |
| *  *           *   * |
| **               * * |
| ******************** |
+----------------------+

画等腰三角形语句

SET @h := 10;       # 高
SET @w := 10;       # 底
SET @x := 0;        # x 座标
SET @y := 0;        # y 座标
SET @k := @w/@h/2;  # 1/2底高比例，即边的斜率的倒数
SET @rate := 2;     # x y 轴比例，调整显示效果 <span>SELECT</span> concat(repeat(<span>" "</span>, @rate * (@w / 2 - (@y - 1) * @k) - 1), <span>"*"</span>, repeat(IF(@y = @h, <span>"*"</span>, <span>" "</span>), @rate * (2 * (@y - 1) * @k) - 1), IF(@y = 1, <span>"", "</span>*")) AS triangle <span>FROM</span> number <span> WHERE</span> (@y := @y + 1) AND @y <= @h;

结果

+---------------------+
| triangle            |
+---------------------+
|          *          |
|         * *         |
|        *   *        |
|       *     *       |
|      *       *      |
|     *         *     |
|    *           *    |
|   *             *   |
|  *               *  |
| ******************* |
+---------------------+

画正弦曲线语句

SET @x := 0;        # x 座标
SET @offset := 15;  # y 偏移
SET @am := 15;      # 振幅
SET @rate := 10;    # x y 轴比例（影响波长），调整显示效果
SET @len := 30;     # 长度 <span> SELECT</span> lpad(<span>"*"</span>, round(@am * sin(@x * 3.14 / @rate) + @offset) + 1, ' ') AS 'sin' <span>FROM</span> number <span>WHERE</span> (@x := @x + 1) < @len;

结果

+---------------------------------+
| sin                             |
+---------------------------------+
|                     *           |
|                         *       |
|                            *    |
|                              *  |
|                               * |
|                              *  |
|                            *    |
|                         *       |
|                     *           |
|                *                |
|           *                     |
|       *                         |
|    *                            |
|  *                              |
| *                               |
|  *                              |
|    *                            |
|       *                         |
|           *                     |
|                *                |
|                     *           |
|                         *       |
|                            *    |
|                              *  |
|                               * |
|                              *  |
|                            *    |
|                         *       |
|                     *           |
+---------------------------------+

画圆语句

SET @r := 12;           # 半径
SET @d := 2 * (@r + 1); # 图形范围，即直径（避免减到0，偏移 1）
SET @x := 0;            # x 座标
SET @y := @r + 1;       # y 座标
SET @rate := 2;         # x y 轴长比例，调整显示效果 <span> SELECT</span> circle <span>FROM</span> ( <span>SELECT</span> @x := round(@rate * sqrt(pow(@r, 2) - pow(@y, 2))) + 1, concat(lpad(<span>"*"</span>, @d - @x, <span>" "</span>), lpad(<span>"*"</span>, 2 * @x, <span>" "</span>)) AS circle <span>FROM</span> number <span>WHERE</span> (@y := @y - 1) > 0 AND @y <= @r
    UNION ALL <span>SELECT</span> @x := round(@rate * sqrt(pow(@r, 2) - pow(@y, 2))) + 1, concat(lpad(<span>"*"</span>, @d - @x, <span>" "</span>), lpad(<span>"*"</span>, 2 * @x, <span>" "</span>)) AS circle <span>FROM</span> number <span>WHERE</span> (@y := @y + 1) > 0 AND @y <= @r
) AS Temp;

结果

+-----------------------------------------------------+
| circle                                              |
+-----------------------------------------------------+
|                         * *                         |
|               *                     *               |
|            *                           *            |
|         *                                 *         |
|       *                                     *       |
|      *                                       *      |
|    *                                           *    |
|   *                                             *   |
|  *                                               *  |
|  *                                               *  |
| *                                                 * |
| *                                                 * |
| *                                                 * |
|  *                                               *  |
|  *                                               *  |
|   *                                             *   |
|    *                                           *    |
|      *                                       *      |
|       *                                     *       |
|         *                                 *         |
|            *                           *            |
|               *                     *               |
|                         * *                         |
+-----------------------------------------------------+

UNION 后再用一个 SELECT 仅是包装一下，看起来像一个整体，不那么松散
回头想想，上面用了 UNION 的都可以用 IF 来整合在一个语句里，不过会显得很臃肿

亚丹
seesea2517#gmail#com
http://seesea.blog.chinaunix.net
http://blog.csdn.net/nicenight
http://my.oschina.net/seesea2517

Statement：

The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Previous article：自动更新日期列的值为最大日期的触发器Next article：T-SQL生成SQL追踪信息

See more

SQL也疯狂：MySQL绘制简单几何图形(2013-04-12)

Related articles