[Original] use the GROUP_CONCAT function of MySQL to implement aggregate Multiplication

The MySQL aggregate function provides addition, average, minimum, and maximum, but not multiplication. Here we use the existing MYSQL GROUP_CONCAT function to implement aggregation multiplication. Create an example Table: CREATETABLE 'tb _ seq '('num' int (10) NOTNULL, 'seq _ type' enum (yellow, green, red) NOTNULL) ENGINEInn

The MySQL aggregate function provides addition, average, minimum, and maximum, but not multiplication. Here we use the existing MYSQL GROUP_CONCAT function to implement aggregation multiplication. Create an example Table: CREATETABLE 'tb _ seq '('num' int (10) NOTNULL, 'seq _ type' enum ('yellow', 'green ', 'red') NOTNULL) ENGINE = Inn

The MySQL aggregate function provides addition, average, minimum, and maximum, but not multiplication. Here we use the existing MYSQL GROUP_CONCAT function to implement aggregation multiplication.

Create an example table first:

CREATE TABLE `tb_seq` (  `num` int(10) NOT NULL,  `seq_type` enum('yellow','green','red') NOT NULL) ENGINE=InnoDB DEFAULT CHARSET=utf8;

Insert sample data:

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');

Create a string multiplication method based on the comma separator, provided that the strings are separated by commas.

DELIMITER $$USE `t_girl`$$DROP FUNCTION IF EXISTS `func_multiple`$$CREATE DEFINER=`root`@`localhost` FUNCTION `func_multiple`(    f_nums VARCHAR(1000)    ) RETURNS DOUBLE(10,2)BEGIN      -- Created by ytt 2014/10/21.      DECLARE result DOUBLE(10,2) DEFAULT 1;      DECLARE cnt,i INT DEFAULT 0;            SET cnt = CHAR_LENGTH(f_nums) - CHAR_LENGTH(REPLACE(f_nums,',','')) + 1;            WHILE i < cnt      DO        -- get multiple result.        SET result = result * REVERSE(SUBSTRING_INDEX(REVERSE(SUBSTRING_INDEX(f_nums,',',i+1)),',',1));        SET i = i + 1;      END WHILE;      SET result = ROUND(result,2);      RETURN result;       END$$DELIMITER ;

Now, we can use the functions I created and the GROUP_CONCAT aggregate function of MYSQL to conveniently implement multiplication.

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)