Question

how can I use Zend_Db_Select to directly select from a subquery (derived table)?

See, I have 5 tables with the same structure, I want to get all rows from them, merge them and remove the duplicates. I am using UNION which removes duplicates automaticly. The problem is that I add a static column to each table before, so there is one column which is different => duplicatation occures.

Here is my query so far:

SELECT `news_main`.*, 'main' as `category` 
FROM `news_main` 
UNION SELECT `news_politics`.*, 'politics' as `category` FROM `news_politics` 
UNION SELECT `news_society`.*, 'society' as `category` FROM `news_society` 
UNION SELECT `news_world`.*, 'world' as `category` FROM `news_world` 
UNION SELECT `news_business`.*, 'business' as `category` FROM `news_business` 
ORDER BY `date` DESC LIMIT 8

See how I add static values to the new column category? Now everything else is the same (there are duplicate rows), but since they are from different categories, UNION can’t remove them.

So I thought I could SELECT all rows from this sub-query and group them to remove duplicates, like this:

SELECT * 
FROM (
    SELECT `news_main`.*, 'main' as `category` 
    FROM `news_main` 
    UNION SELECT `news_politics`.*, 'politics' as `category` FROM `news_politics`
    UNION SELECT `news_society`.*, 'society' as `category` FROM `news_society` 
    UNION SELECT `news_world`.*, 'world' as `category` FROM `news_world` 
    UNION SELECT `news_business`.*, 'business' as `category` FROM `news_business` 
    ORDER BY `date` DESC LIMIT 8
) as subtable 
GROUP BY `source` 
ORDER BY `date` DESC

I did run this in MySQL and it works perfectly.. the only problem is….

How do I execute this using Zend_Db_Select’s fancy functions?

Thanks in advance!

Answer 1

I’m not sure if you can use nesting selects in the from construct of Zend_Db_Select or if you should even be doing it that way, but an alternative solution would be to just get the db adapter and build the sql query manually.

$db = Zend_Db_Table::getDefaultAdapter();
$db->query("SELECT * 
    FROM (
        SELECT `news_main`.*, 'main' as `category` 
        FROM `news_main` 
        UNION SELECT `news_politics`.*, 'politics' as `category` FROM `news_politics`
        UNION SELECT `news_society`.*, 'society' as `category` FROM `news_society` 
        UNION SELECT `news_world`.*, 'world' as `category` FROM `news_world` 
        UNION SELECT `news_business`.*, 'business' as `category` FROM `news_business` 
        ORDER BY `date` DESC LIMIT 8
    ) as subtable 
    GROUP BY `source` 
    ORDER BY `date` DESC
");

related:
Zend_Db_Table subquery