how can I get a field value in 3 association tables with the max of date

问题

So, I have a table and I want to get the value from one field in the record with the greatest DateTime() value in another field and where still another field is equal to a certain value.

    --
    -- Structure de la table `site`
    --
    CREATE TABLE IF NOT EXISTS `site` (
      `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
      `site_name` varchar(15) NOT NULL,
      `city` varchar(50) DEFAULT NULL,
      `address` varchar(80) DEFAULT NULL,
      `entity` varchar(50) DEFAULT NULL,
      `status_activity` tinyint(1) NOT NULL DEFAULT '1',
      `infra` tinyint(1) NOT NULL DEFAULT '0',
      PRIMARY KEY (`id`),
      KEY `idx_site_name` (`site_name`)
    ) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=3 ;

    --
    -- Contenu de la table `site`
    --

    INSERT INTO `site` (`id`, `site_name`, `city`, `address`, `entity`, `status_activity`, `infra`) VALUES
    (1, 'FR001', 'tttt', 'tttttttttt', 'yyyyy', 1, 0),
    (2, 'FR002', 'ccccc', 'cccccccccc', 'rrrrrrrrrrrr', 1, 0);

    -- --------------------------------------------------------

    --
    -- Structure de la table `site_topology`
    --

    CREATE TABLE IF NOT EXISTS `site_topology` (
      `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
      `id_site` int(10) unsigned NOT NULL,
      `id_topology` int(10) unsigned NOT NULL,
      `date` date NOT NULL,
      PRIMARY KEY (`id`),
      KEY `idx_site_date` (`date`),
      KEY `fk_id_site_2` (`id_site`),
      KEY `fk_id_topology_2` (`id_topology`)
    ) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=7 ;

    --
    -- Contenu de la table `site_topology`
    --

    INSERT INTO `site_topology` (`id`, `id_site`, `id_topology`, `date`) VALUES
    (1, 1, 1, '2015-03-03'),
    (2, 2, 3, '2015-03-03'),
    (3, 1, 2, '2015-04-30'),
    (4, 2, 5, '2015-04-30'),
    (5, 1, 1, '2015-06-25'),
    (6, 2, 4, '2015-06-25');

    -- --------------------------------------------------------

    --
    -- Structure de la table `topology`
    --

    CREATE TABLE IF NOT EXISTS `topology` (
      `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
      `name` varchar(10) NOT NULL,
      PRIMARY KEY (`id`),
      KEY `idx_type_name` (`name`)
    ) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=7 ;

    --
    -- Contenu de la table `topology`
    --

    INSERT INTO `topology` (`id`, `name`) VALUES
    (3, 'C1/C2'),
    (2, 'C3'),
    (5, 'HBN'),
    (4, 'Infrastruc'),
    (6, 'LB'),
    (1, 'SHBN');

    --
    -- Contraintes pour les tables exportées
    --

    --
    -- Contraintes pour la table `site_topology`
    --
    ALTER TABLE `site_topology`
      ADD CONSTRAINT `fk_id_site_2` FOREIGN KEY (`id_site`) REFERENCES `site` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
      ADD CONSTRAINT `fk_id_topology_2` FOREIGN KEY (`id_topology`) REFERENCES `topology` (`id`) ON DELETE CASCADE ON UPDATE CASCADE

I want to see

FR001 SHBN 2015-06-26
FR002 Infrastruct 2015-06-26

but when I execute my query I have this

FR001 SHBN 2015-06-26`enter code here`
FR002 C1/C2 2015-06-26    

Can anyone help me?

回答1:

You had a problem on how to choose the max date, since the month was showing first. A different way is to bring up the max_date value (from a sub-query). After it you can compare by the different parts of the date. Code as follows:

select site_name, site_date, name 
 from
  (
    select  site_name, st.date as site_date, name, s.id, (select max(sto.date) from site_topology sto) as max_date
    from site s 
     inner join site_topology st on s.id =st.id_site
     inner join topology t on st.id_topology = t.id 
  )  as v
 where YEAR(site_date) = YEAR(max_date) AND MONTH(site_date) = MONTH(max_date) AND DAY(site_date) = DAY(max_date)
 group by name
 order by site_name

Testing here.

回答2:

use a subquery they're correct's aggregate Results here

select site_name,max(date), name 
   from
    (select  site_name, 
     city, address, entity , status_activity, infra,
     st.*,name
     from site s 
       inner join site_topology st on s.id =st.id_site
       inner join topology t on st.id_topology = t.id ) 
     as v
   group by site_name

来源：https://stackoverflow.com/questions/29297793/how-can-i-get-a-field-value-in-3-association-tables-with-the-max-of-date