wordpress query_posts to look at meta info

I am looking to run a query with query_posts that lets me look at meta_fields. I have done this once before and achieved the result I wanted but now for some reason adding an extra field into the equation returns nothing.

The query below returns all attachments where the lottery_year is equal to $y, and obviously $y can be 2011 or earlier.

Now my next step I want to bring in another meta_field called photo_technique and give that one a value.

Question, how do I do that?

$querystr = "
    SELECT $wpdb->posts.*
    FROM $wpdb->posts
    LEFT JOIN $wpdb->postmeta ON ($wpdb->posts.ID = $wpdb->postmeta.post_id)
    WHERE ($wpdb->postmeta.meta_key = 'lottery_year' AND $wpdb->postmeta.meta_value = $y)
    AND $wpdb->posts.p开发者_高级运维ost_type = 'attachment'
    ORDER BY $wpdb->postmeta.meta_value ASC
    LIMIT 100
";

If you whant to display posts that have either lottery_year = $y ( or ) photo_technique = $x, you could use :

$querystr = "
    SELECT $wpdb->posts.*
    FROM $wpdb->posts
    LEFT JOIN $wpdb->postmeta ON ($wpdb->posts.ID = $wpdb->postmeta.post_id)
    WHERE ($wpdb->postmeta.meta_key = 'lottery_year' AND $wpdb->postmeta.meta_value = $y) OR ($wpdb->postmeta.meta_key = 'photo_technique' AND $wpdb->postmeta.meta_value = $x)
    AND $wpdb->posts.post_type = 'attachment'
    ORDER BY $wpdb->postmeta.meta_value ASC
    LIMIT 100
";

Edit

If you whant to display results that have both lottery_year = $y ( AND ) photo_technique = $x, you could use the following query :

$querystr = "
    SELECT
        $wpdb->posts.*
    FROM 
        $wpdb->posts
    INNER JOIN $wpdb->postmeta ON
        $wpdb->posts.ID = $wpdb->postmeta.post_id 
        AND $wpdb->postmeta.meta_key IN ( 'lottery_year', 'photo_technique' )
        AND $wpdb->postmeta.meta_value IN ( '$y', '$x' )
    WHERE $wpdb->posts.post_type = 'attachment'
    GROUP BY $wpdb->posts.ID
    HAVING COUNT(1) = 2
    ORDER BY $wpdb->postmeta.meta_value ASC
    LIMIT 100
";

Edit

The last query ( the AND one ) will fail in some circumstances. For example you whant lottery_year = $y AND photo_technique = $x, but it will allso return results that have the $x and $y switched like : lottery_year = $x AND photo_technique = $y, it realy depends when you can rely on it or not, like do you have a photo_technique that is called for example '2001' ( witch could pass as a lottery_year too ) . Please be carefull with it or ask this question on dba.stackexchange.com or wordpress.stackexchange.com .