MySQL 聚合函數(shù)里面提供了加，平均數(shù)，最小，最大等，但是沒(méi)有提供乘法，我們這里來(lái)利用MYSQL現(xiàn)有的GROUP_CONCAT函數(shù)實(shí)現(xiàn)聚合乘法。

先創(chuàng)建一張示例表：CREATE?TABLE?`tb_seq`?(

`num`?int(10)?NOT?NULL,

`seq_type`?enum('yellow','green','red')?NOT?NULL

)?ENGINE=InnoDB?DEFAULT?CHARSET=utf8;

插入示例數(shù)據(jù)：insert??into?`tb_seq`(`num`,`seq_type`)

values?(4,'green'),(1,'red'),(3,'green'),

(1,'red'),(8,'red'),(4,'yellow'),

(8,'red'),(7,'yellow'),(10,'red'),

(1,'red'),(1,'red'),(1,'yellow'),

(5,'green'),(9,'red'),(1,'yellow'),

(6,'yellow');

創(chuàng)建基于逗號(hào)分隔符的字符串乘法，前提是字符串逗號(hào)分隔的都是數(shù)字。DELIMITER?$$

USE?`t_girl`$$

DROP?FUNCTION?IF?EXISTS?`func_multiple`$$

CREATE?DEFINER=`root`@`localhost`?FUNCTION?`func_multiple`(

f_nums?VARCHAR(1000)

)?RETURNS?DOUBLE(10,2)

BEGIN

--?Created?by?ytt?2014/10/21.

DECLARE?result?DOUBLE(10,2)?DEFAULT?1;

DECLARE?cnt,i?INT?DEFAULT?0;

SET?cnt?=?CHAR_LENGTH(f_nums)?-?CHAR_LENGTH(REPLACE(f_nums,',',''))?+?1;

WHILE?i?

DO

--?get?multiple?result.

SET?result?=?result?*?REVERSE(SUBSTRING_INDEX(REVERSE(SUBSTRING_INDEX(f_nums,',',i+1)),',',1));

SET?i?=?i?+?1;

END?WHILE;

SET?result?=?ROUND(result,2);

RETURN?result;

END$$

DELIMITER?;

好了，我們利用我創(chuàng)建的函數(shù)以及MYSQL自帶的GROUP_CONCAT聚合函數(shù)就可以很方便的實(shí)現(xiàn)乘法了。SELECT?seq_type,func_multiple(GROUP_CONCAT(num?ORDER?BY?num?ASC?SEPARATOR?','))?AS?multiple_num?FROM?tb_seq?WHERE?1?GROUP?BY?seq_type;

+----------+--------------+

|?seq_type?|?multiple_num?|

+----------+--------------+

|?yellow???|???????168.00?|

|?green????|????????60.00?|

|?red??????|??????5760.00?|

+----------+--------------+

3?rows?in?set?(0.00?sec)

總結(jié)

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