SQL-基于同一表中的另一个值排除一行

Question

The application in question is a classified site. I'm using a query to retrieve a value in a field called "cp_price" to generate a total value for all the listings in the system.

My goal is to exclude all listings that have a value of "yes" in the "cp_ad_sold" field.

Here's the query I'm using to retrieve the values:

$raw_prices = $wpdb->get_col( $wpdb->prepare( "     
    SELECT pm.meta_value FROM {$wpdb->postmeta} AS pm 
    LEFT JOIN {$wpdb->posts} AS p ON p.ID = pm.post_id 
    WHERE p.post_type = 'ad_listing'
    AND p.ID = pm.post_id
    AND pm.meta_key = 'cp_price'
    " ) );

So, I am guessing I need to do a subselect?

I know that the key and respective value I need is stored in the postmeta table, right along with the "cp_price" field. I also know that "cp_price" and "cp_ad_sold" share the same "post_id".

Question: How do I go about excluding the ad_listings and their respective cp_price value, based on a value of "yes" in the key of "cp_ad_sold"?

Note: I'm using WordPress for this and considered posting the question over on the WordPress Stackexchange. I figured this was a heavily SQL based question, though, and figured this was the most appropriate venue.

Answer 1

You may also want to add a condition to the WHERE clause -

$raw_prices = $wpdb->get_col( $wpdb->prepare( "     
    SELECT pm.meta_value FROM {$wpdb->postmeta} AS pm 
    LEFT JOIN {$wpdb->posts} AS p ON p.ID = pm.post_id 
    WHERE p.post_type = 'ad_listing'
    AND p.ID = pm.post_id -- Do you really need it? Check LEFT JOIN ... ON clause
    AND pm.meta_key = 'cp_price'
    AND cp_ad_sold <> 'yes' -- Something like this
    " ) );