create trigger which inserts rows depending on enum values?

Question

I'm quite new to triggers and I ran into general problems. I'd like to achieve this:

CREATE TABLE `searcharticles` (
 `articleID` int(11) unsigned NOT NULL,
 `ean` char(13) COLLATE utf8_unicode_ci DEFAULT NULL,
 `manufacturerNumber` varchar(20) COLLATE utf8_unicode_ci NOT NULL,  
 PRIMARY KEY (`articleID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci


CREATE TABLE `addresses` (
 `articleID` int(11) unsigned NOT NULL,
 `shop` enum('shop1','shop2') COLLATE utf8_unicode_ci NOT NULL,
 `url` varchar(255) COLLATE utf8_unicode_ci NULL,
 `status` tinyint(3) NOT NULL DEFAULT '0',
 `createTime` datetime NOT NULL,
 `updateTime` timestamp NULL DEFAULT NULL ON UPDATE CURRENT_TIMESTAMP,
 PRIMARY KEY (`articleID`,`shop`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci 

When a new row is inserted in searcharticles, the table addresses should be filled, but not only once. I'd like to make a record for every shop that is in enum shop (I know this is not well designed). I'm stuck at this:

CREATE TRIGGER ins_addresses AFTER INSERT on searcharticles
FOR EACH ROW
BEGIN
  INSERT INTO addresses(articleID, shop, createtime) VALUES(NEW.articleID, ?, CURRENT_TIMESTAMP);
END

How could I iterate through the possible enum values to trigger an insert with 'shop1' and another with 'shop2' without writing a possible shop name in the insert?

Answer 1

It's not pretty, but this gets the possible enum values from INFORMATION_SCHEMA.COLUMNS.

DELIMITER $$

DROP TRIGGER ins_addresses $$

CREATE TRIGGER ins_addresses AFTER INSERT on searcharticles
FOR EACH ROW
BEGIN

DECLARE column_list char(200);
DECLARE current_value char(200);
DECLARE counter INT DEFAULT 0;
DECLARE num_enums INT;

  /* Format goes from "enum('shop1','shop2')" to "shop1,shop2" */

  SELECT REPLACE(SUBSTR(COLUMN_TYPE,6,LENGTH(COLUMN_TYPE)-6),'''','')
  FROM INFORMATION_SCHEMA.COLUMNS 
  WHERE TABLE_SCHEMA = 'stackex' 
  AND TABLE_NAME = 'addresses' 
  AND COLUMN_NAME = 'shop'
  INTO column_list;

  SET num_enums = LENGTH(column_list)- LENGTH(REPLACE(column_list, ',', ''))+1;

  WHILE counter < num_enums DO
    SET current_value = (SELECT REPLACE(SUBSTRING(SUBSTRING_INDEX(column_list, ',', counter+1),
          LENGTH(SUBSTRING_INDEX(column_list, ',', counter )) + 1), ',', ''));

    INSERT INTO addresses(articleID, shop, createtime)
    VALUES (NEW.articleID, current_value, CURRENT_TIMESTAMP);

    SET counter = counter + 1;  
  END WHILE;
END$$
DELIMITER ;

Test:

mysql> use stackex;
Database changed
mysql> insert into searcharticles values ( 1, 'foo','bar' );
Query OK, 1 row affected (0.00 sec)

mysql> select * from addresses;
+-----------+-------+------+--------+---------------------+------------+
| articleID | shop  | url  | status | createTime          | updateTime |
+-----------+-------+------+--------+---------------------+------------+
|         1 | shop1 | NULL |      0 | 2012-08-17 09:32:33 |       NULL |
|         1 | shop2 | NULL |      0 | 2012-08-17 09:32:33 |       NULL |
+-----------+-------+------+--------+---------------------+------------+
2 rows in set (0.00 sec)

mysql>

I actually hate myself for answering this! Change the data model to use a lookup table, shops.

It'll break horribly if the shop enum names have commas or quotation marks in them (probably).