Question

我有以下架构，表示存储在MySQL中的图形。

Nodes

Id | Type


Links
Id | Source_id | Dest_id

其中source_id和dest_id是Nodes表的外键。每个节点都可以有多个链接。

我想创建一个存储过程来从图中节点的给定id开始检索子图。我正在查看此示例http://sqlfiddle.com/#!2/58c804/1，但仅当每个节点都有一个链接时才有效。我想我应该使用CURSOR，但我不知道如何让它发挥作用。

@C_B我尝试的是以下内容：

我有以下树：

            5
            |
            1
          /    \
         2      3 
        /
       4

CREATE TABLE Nodes
      (`id` int, `type` varchar(10))

CREATE TABLE Links
      (`id` int, `source_id` int, `dest_id` int)

INSERT INTO Nodes
     (`id`, `type`)
VALUES
     (1, 'a'),
     (2, 'b'),
     (3, 'c'),
     (4, 'd'),
     (5, 'e')

INSERT INTO Links
     (`id`, `source_id`, `dest_id`)
VALUES
     (1, 1, 2),
     (2, 1, 3),
     (3, 2, 4),
     (4, 5, 1)


CREATE PROCEDURE get_subgraph(IN id int)
BEGIN
DECLARE prev_id int;
DECLARE child_id int;
DECLARE done INT DEFAULT FALSE; 
SET prev_id = id;
DECLARE child_cursor CURSOR FOR 
SELECT dest_id FROM Links WHERE source_id=prev_id ;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
OPEN child_cursor;
FETCH child_cursor INTO child_id;
CREATE TEMPORARY TABLE IF NOT EXISTS results AS (SELECT * FROM Links WHERE 1=0);
TRUNCATE TABLE results

WHILE child_id <> 0 DO
     INSERT INTO results SELECT * FROM Links WHERE source_id=prev_id;
     SET prev_id = child_id;
     SET child_id=0;
     FETCH child_cursor INTO child_id;
     IF done THEN
         SET done = FALSE;
         CLOSE child_cursor;
         DECLARE child_cursor CURSOR FOR 
         SELECT dest_id FROM results WHERE source_id=prev_id;
         DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
         OPEN child_cursor;
         FETCH child_cursor INTO child_id;
     END IF
END WHILE;
SELECT * FROM results;
END

我想打电话 CALL get_subgraph（1）;

并得到以下结果：

结果

id | source_id | dest_id
1  | 1         | 2
2  | 1         | 3
3  | 2         | 4

非常感谢您的帮助

创建从MYSQL中提取子图的过程

0 个答案: