Question

I have this table built like this, which assigns a unique articleId starting with zero for each user.

CREATE TABLE `articles` (
  `artcId` INT(10) NOT NULL AUTO_INCREMENT,
  `artcUserId` INT(10) NOT NULL DEFAULT '0',
  `artcStackId` INT(10) NOT NULL DEFAULT '0',
  `artcTitle` VARCHAR(200) NULL DEFAULT NULL,
  PRIMARY KEY (`artcUserId`, `artcId`)
)
COLLATE='utf8_general_ci'
ENGINE=MyISAM;

There also is a part which assigns a running serial number (artcStackId) to each article. You’ll see in the code.

Thing is, is it somehow possible to assign a artcStackId based on the country of the user? That country code will come from php.

Eg: If it’s US then start from 10001+1, if its UK start from 20001+1, if its CA then start from 30001+1 and on & on.

Will it be possible to do this?

My current SQL query goes as follows:

insert into articles (artcUserId, artcStackId, artcCountry, artcTitle)
select 4,IFNULL((MAX(artcStackId)+1) ,0),'US','Hello World'
FROM articles;

But the way I want it it’ll have to go like (this is just an example sql):

insert into articles (artcUserId, artcStackId, artcCountry, artcTitle)
select 4, IF artcCountry = 'US' then (selct MAX(artcStackId)+1
                                      where artcCountry = 'US'),
       'US','Hello World'
FROM articles;

I hope you get the idea.

Answer 1

I would suggest you to use a TRIGGER:

CREATE TRIGGER ins_articles
BEFORE INSERT ON articles
FOR EACH ROW
  SET new.artcStackId=coalesce(
    (select max(artcStackId)
    from articles
    where artcCountry = new.artcCountry)+1,1)
;

or something like this:

CREATE TRIGGER ins_articles
BEFORE INSERT ON articles
FOR EACH ROW
  SET new.artcStackId=coalesce(
    (select max(artcStackId)
    from articles
    where artcCountry = new.artcCountry)+1,

    case when new.artcCountry = 'US' then 10001
         when new.artcCountry = 'UK' then 20001
         when new.artcCountry = 'CA' then 30001
    end)
;

see it working here. Then you can insert without specifying the column artcStackId, since it will automatically be calculated.