SELECT表并从另一个表获取一些数据（如果存在）

Question

Anybody can tell me if following scenario is possible to achieve in Doctrine (and generaly in mysql)?

Scenario: I've got table cms_pages with fields like:

• id
• cms_languages_id
• name
• content
• alias

And another table called cms_pages_translations with fields like:

• id
• cms_pages_id (foreign key)
• cms_languages_id
• name
• content
• alias

And now, let say, that

 $language_id = 2;

I'm querying cms_pages and see, that cms_pages.cms_languages_id is not equals to $language_id... (So my page content is not in language that I'm looking for). But it's OK. We got a table called cms_pages_translations where translation should be present. So I want to, in the same query to get matching values (name, content,alias) from cms_pages_translations if there is record with

cms_languages_id == $language_id.

I hope It's clear what I want to achieve :)

So query output data will contain:

• id (from cms_pages)
• name (from cms_pages_translations )
• content (from cms_pages_translations )
• alias (from cms_pages_translations )

Answer 1

if cms_pages_id is foreign key for cms_pages.id then why don't you just query in cms_pages_translations as all translations should present in this table. i think you should have $page_id to get any specific page translation.

you can use following query

SELECT id, NAME, content, alias FROM cms_pages WHERE id=1 AND cms_languages_id = 2
UNION
SELECT cms_pages_id, NAME, content, alias FROM cms_pages_translations WHERE cms_pages_id=1 AND cms_languages_id = 2 AND 0 = (SELECT COUNT(id) FROM cms_pages WHERE id=1 AND cms_languages_id = 2);

but this again scan cms_pages_translations for every case. best thing for you is fire 2 queries conditional (as mentioned in comment) and create an index on cms_pages_translations (cms_pages_id, cms_languages_id)

Answer 2

you can try an IFNULL construction, like:

SELECT IFNULL(
    (SELECT content FROM cms_pages WHERE cms_languages_id=3 AND id=1), 
    (SELECT content FROM cms_pages_translations WHERE cms_languages_id=3 AND id=1)
  )

the only point with this is, IFNULL can only retrun one column at a time. so you may query each colum seperatly.

or u try a JOIN like this:

SELECT *
FROM cms_pages_translations t 
JOIN cms_pages p ON p.id=t.cms_pages_id
WHERE t.id=1 AND (t.cms_languages_id=1 OR p.cms_languages_id=1)

which will return all fields of both tables if they exist. assuming that data for "name", "alias" and "content" will only be present in one of both tables for oone pageID this will do it.

Answer 3

You can try using MySQL Case . As I remember it can't be used in Zend directly, so I used it with Zend_Db_Expr .

public function getPageTranslated($page_id, $language_id) {
    $name = new Zend_Db_Expr("
        CASE 
            WHEN p.language_id = $language_id THEN p.name
            ELSE pt.name
        END
    ");

    $content = new Zend_Db_Expr("
        CASE 
            WHEN p.language_id = $language_id THEN p.content
            ELSE pt.content
        END
    ");

    $alias = new Zend_Db_Expr("
        CASE 
            WHEN p.language_id = $language_id THEN p.alias
            ELSE pt.alias
        END
    ");

    $select = $this->select()
            ->from(array('p' => 'cms_pages'), array('id' => 'p.id', 'name' => $name, 'content' => $content, 'alias' => $alias))
            ->where('p.id = ?', $page_id)
            ->joinLeft(array('pt' => 'cms_pages_translations'), 'p.id = pt.cms_pages_id', array('pt.name', 'pt.content', 'pt.alias'))
            ->where('pt.language_id = ?', $language_id)
            ->limit(1)
            ->setIntegrityCheck(false);

    $result = $this->fetchAll($select);

    return $result? $result->toArray(): false;
}