MySQL / WordPress元查询； 结合多个条件

Question

Apologies if this is fairly basic, I'm a little out of my depth and could use a bit of guidance to fill in some blanks.

Here's the situation... I'm querying the WordPress database to return a subset of posts which match a set of specific criteria relating to meta key/value conditions (specifically, whether a key of 'dates' contains a value which matches the next X days). This works fine - the code is currently:

$request  = "SELECT DISTINCT ID FROM $wpdb->posts, $wpdb->postmeta";
$request .= " WHERE $wpdb->posts.ID = $wpdb->postmeta.post_id";
$request .= " AND post_status='publish' AND post_type='days'";
$request .= " AND $wpdb->postmeta.meta_key = 'dates' AND $wpdb->postmeta.meta_value >= '$startDate' AND $wpdb->postmeta.meta_value <= '$endDate' AND $wpdb->postmeta.meta_value != '$today'";

Now, I'd like to introduce another scenario, and also return any posts which have a key of *_dayType*, and a value of month , where month is the current month. I've extended the code to allow for an OR rule to also return posts which match the first day of the month. The extended code looks like:

$request  = "SELECT DISTINCT ID FROM $wpdb->posts, $wpdb->postmeta";
$request .= " WHERE $wpdb->posts.ID = $wpdb->postmeta.post_id";
$request .= " AND post_status='publish' AND post_type='days'";
$request .= " AND ";
$request .= " (($wpdb->postmeta.meta_key = 'dates' AND $wpdb->postmeta.meta_value >= '$startDate' AND $wpdb->postmeta.meta_value <= '$endDate' AND $wpdb->postmeta.meta_value != '$today')";
$request .= " OR ";
$request .= " ($wpdb->postmeta.meta_key = 'dates' AND $wpdb->postmeta.meta_value = '$firstDayOfMonth' ))";

Now I run into a problem. I want to expand the conditions for returning the new month posts by querying the meta_key variable again. Eg,

$wpdb->postmeta.meta_key = '_dayType' AND $wpdb->postmeta.meta_value = 'month'

However, adding this in returns zero results. I've tested querying just one of the conditions (either matching the first day of the month, or matching being a month ), and I can return one or the other with no problem. I'm pretty sure that the problem is that I'm querying the same variable twice in the same string, with no consideration for ordering or distinction. What's the best way of reconstructing this query to bring back:

• Posts which match the next X days OR
• Posts which are 'months'

Here's the final mark-up. Is the problem just my AND nesting syntax?

$request  = "SELECT DISTINCT ID FROM $wpdb->posts, $wpdb->postmeta";
$request .= " WHERE $wpdb->posts.ID = $wpdb->postmeta.post_id";
$request .= " AND post_status='publish' AND post_type='days'";
$request .= " AND ";
$request .= " (($wpdb->postmeta.meta_key = 'dates' AND $wpdb->postmeta.meta_value >= '$startDate' AND $wpdb->postmeta.meta_value <= '$endDate' AND $wpdb->postmeta.meta_value != '$today')";
$request .= " OR ";
$request .= " (($wpdb->postmeta.meta_key = 'dates' AND $wpdb->postmeta.meta_value = '$firstDayOfMonth') AND ($wpdb->postmeta.meta_key = '_daytype' AND $wpdb->postmeta.meta_value = 'month')) )";

Answer 1

Resolved; needed to query multiple keys via OR, rather than AND, as the variable couldn't have two values at once now, could it?

SELECT DISTINCT ID FROM wp_posts, wp_postmeta 
WHERE (
 wp_posts.ID = wp_postmeta.post_id
 AND post_status = 'publish'
 AND post_type = 'days'
 AND (
  wp_postmeta.meta_key = 'dates' 
  AND wp_postmeta.meta_value >= '$startDate' 
  AND wp_postmeta.meta_value <= '$endDate' 
  AND wp_postmeta.meta_value != '$today'
 )
)
UNION
SELECT DISTINCT ID FROM wp_posts, wp_postmeta 
WHERE (
 wp_posts.ID = wp_postmeta.post_id
 AND post_status = 'publish'
 AND post_type = 'days'
 AND (
 (wp_postmeta.meta_key = '_dayType' AND wp_postmeta.meta_key = 'month')
 OR
 (wp_postmeta.meta_key = 'dates' AND wp_postmeta.meta_value = '$firstDayOfMonth' )
 )
)