我有以下存储过程,用于实现Dijkstra的最短路径算法:
CREATE PROCEDURE `Dijkstras`(IN `pids` VARCHAR(512), IN `startP` VARCHAR(8), IN `endP` VARCHAR(8), OUT `dist` DECIMAL(20,10), OUT `eset` VARCHAR(1024))
BEGIN
DECLARE currentP VARCHAR(4);
DECLARE finished INT DEFAULT 0;
DECLARE pt_from, pt_to int;
DECLARE pt_dist decimal(20,10);
DECLARE done INT DEFAULT 0;
DECLARE cur2 CURSOR FOR
select F.id as `from`, T.id as `to`, dist(F.lat, F.lng, T.lat, T.lng)
as dist
from sampledata F, sampledata T
where F.id < T.id and
find_in_set(convert(F.id, char(10)), pids) and
find_in_set(convert(T.id, char(10)), pids)
order by dist;
DECLARE CONTINUE HANDLER FOR not found SET done = 1;
SET currentP= startP;
SET eset = '';
SET dist = 0;
SET done=0;
OPEN cur2; -- this finds pariwise distances in miles.
REPEAT
FETCH cur2 INTO pt_from, pt_to, pt_dist;
SET dist= dist+pt_dist;
SET eset= CONCAT(eset, ',');
IF(currentP=pt_from OR currentP=pt_to) AND
(IN_SET(pt_from,pids) AND IN_SET(pt_to,pids)) THEN
BEGIN
SET dist= dist+ pt_dist;
SET pids= REMOVE_MEMBER(currentP, pids);
SET eset = concat(eset, ',', concat(pt_from, ':', pt_to));
IF left(eset, 1) = ',' then
SET eset = substring(eset, 2); -- remove extra comma.
END IF;
IF currentP=pt_from THEN
SET currentP=pt_to;
ELSE
SET currentP=pt_from;
END IF;
IF currentP= endP THEN
SET finished= 1;
END IF;
END;
END IF;
UNTIL done
END REPEAT;
CLOSE cur2;
END
我的问题是光标无法正常工作。当我将当前行提取到pt_from, pt_to,
和pt_dist
时,我得到的是NULL
值。 sampledata
表正确存储在数据库中,pids
中的所有点ID也都在sampledata
表中。此外,这个EXACT代码适用于另一个程序,但在此重复使用它是行不通的。
有人知道我做错了吗?
答案 0 :(得分:0)
错误是我传递了像这个'12, 15, 18'
的点ID,其间有空格。 MySQL在解析字符串时计算空白,并且列表中的id没有空格。传递字符串集的正确方法是'12,15,18'
。