我遇到了這個問題，並意識到問題是所有由WordPress生成的INNER JOINS。我得到了WordPress的原始查詢：
SELECT wp_posts.* FROM wp_posts
INNER JOIN wp_term_relationships ON (wp_posts.ID = wp_term_relationships.object_id)
INNER JOIN wp_postmeta ON (wp_posts.ID = wp_postmeta.post_id)
INNER JOIN wp_postmeta AS mt1 ON (wp_posts.ID = mt1.post_id)
INNER JOIN wp_postmeta AS mt2 ON (wp_posts.ID = mt2.post_id)
INNER JOIN wp_postmeta AS mt3 ON (wp_posts.ID = mt3.post_id)
INNER JOIN wp_postmeta AS mt4 ON (wp_posts.ID = mt4.post_id)
INNER JOIN wp_postmeta AS mt5 ON (wp_posts.ID = mt5.post_id) WHERE 1=1 AND (wp_term_relationships.term_taxonomy_id IN (7,11,12,13,14,15) AND wp_posts.ID NOT IN (
SELECT object_id
FROM wp_term_relationships
WHERE term_taxonomy_id IN (10)
)) AND wp_posts.post_type IN ('post', 'page', 'attachment', 'product', 'store_page') AND (wp_posts.post_status = 'publish') AND ((wp_postmeta.meta_key = 'product_type' AND CAST(wp_postmeta.meta_value AS CHAR) = 'type_pre_ground')
OR (mt1.meta_key = 'product_type2' AND CAST(mt1.meta_value AS CHAR) = 'type_pre_ground')
OR (mt2.meta_key = 'product_type3' AND CAST(mt2.meta_value AS CHAR) = 'type_pre_ground')
OR (mt3.meta_key = 'product_type4' AND CAST(mt3.meta_value AS CHAR) = 'type_pre_ground')
OR (mt4.meta_key = 'product_type5' AND CAST(mt4.meta_value AS CHAR) = 'type_pre_ground')
OR (mt5.meta_key = 'product_type6' AND CAST(mt5.meta_value AS CHAR) = 'type_pre_ground')) GROUP BY wp_posts.ID ORDER BY wp_posts.post_date DESC
這從來沒有完成，並在非常高的負載捆綁CPU。我刪除了過去兩年內連接（以及相應的WHERE子句），並得到了2秒的成績：
SELECT wp_posts.* FROM wp_posts
INNER JOIN wp_term_relationships ON (wp_posts.ID = wp_term_relationships.object_id)
INNER JOIN wp_postmeta ON (wp_posts.ID = wp_postmeta.post_id)
INNER JOIN wp_postmeta AS mt1 ON (wp_posts.ID = mt1.post_id)
INNER JOIN wp_postmeta AS mt2 ON (wp_posts.ID = mt2.post_id)
INNER JOIN wp_postmeta AS mt3 ON (wp_posts.ID = mt3.post_id) WHERE 1=1 AND (wp_term_relationships.term_taxonomy_id IN (7,11,12,13,14,15) AND wp_posts.ID NOT IN (
SELECT object_id
FROM wp_term_relationships
WHERE term_taxonomy_id IN (10)
)) AND wp_posts.post_type IN ('post', 'page', 'attachment', 'product', 'store_page') AND (wp_posts.post_status = 'publish') AND ((wp_postmeta.meta_key = 'product_type' AND CAST(wp_postmeta.meta_value AS CHAR) = 'type_pre_ground')
OR (mt1.meta_key = 'product_type2' AND CAST(mt1.meta_value AS CHAR) = 'type_pre_ground')
OR (mt2.meta_key = 'product_type3' AND CAST(mt2.meta_value AS CHAR) = 'type_pre_ground')
OR (mt3.meta_key = 'product_type4' AND CAST(mt3.meta_value AS CHAR) = 'type_pre_ground')) GROUP BY wp_posts.ID ORDER BY wp_posts.post_date DESC
所以我意識到，去除內連接的關鍵是加快查詢。我重新寫了查詢，只有一個wp_postmeta INNER JOIN和在幾分之一秒內得到結果：
SELECT wp_posts.* FROM wp_posts
INNER JOIN wp_term_relationships ON (wp_posts.ID = wp_term_relationships.object_id)
INNER JOIN wp_postmeta ON (wp_posts.ID = wp_postmeta.post_id) WHERE 1=1 AND (wp_term_relationships.term_taxonomy_id IN (7,11,12,13,14,15) AND wp_posts.ID NOT IN (
SELECT object_id
FROM wp_term_relationships
WHERE term_taxonomy_id IN (10)
))
AND wp_posts.post_type IN ('post', 'page', 'attachment', 'product', 'store_page')
AND (wp_posts.post_status = 'publish')
AND ((wp_postmeta.meta_key = 'product_type' AND CAST(wp_postmeta.meta_value AS CHAR) = 'type_pre_ground')
OR (wp_postmeta.meta_key = 'product_type2' AND CAST(wp_postmeta.meta_value AS CHAR) = 'type_pre_ground')
OR (wp_postmeta.meta_key = 'product_type3' AND CAST(wp_postmeta.meta_value AS CHAR) = 'type_pre_ground')
OR (wp_postmeta.meta_key = 'product_type4' AND CAST(wp_postmeta.meta_value AS CHAR) = 'type_pre_ground')
OR (wp_postmeta.meta_key = 'product_type5' AND CAST(wp_postmeta.meta_value AS CHAR) = 'type_pre_ground')
OR (wp_postmeta.meta_key = 'product_type6' AND CAST(wp_postmeta.meta_value AS CHAR) = 'type_pre_ground'))
GROUP BY wp_posts.ID ORDER BY wp_posts.post_date DESC
有了這個解決方案，我創建了一個WordPress的過濾器的postmeta查詢轉換爲更快的格式：
function custom_get_meta_sql($meta_sql)
{
global $wpdb;
$posts_table = $wpdb->prefix . 'posts';
$postmeta_table = $wpdb->prefix . 'postmeta';
//use single INNER JOIN
$meta_sql['join'] = " INNER JOIN {$postmeta_table} AS pmta ON ({$posts_table}.ID = pmta.post_id) ";
//replace the mtNN aliases with wp_postmeta
$where_clause = $meta_sql['where'];
$where_clause = str_replace("{$postmeta_table}.", 'pmta.', $where_clause);
$where_clause = preg_replace('/mt\d+\.meta_/i', 'pmta.meta_', $where_clause);
$meta_sql['where'] = $where_clause;
return $meta_sql;
}
add_filter('get_meta_sql', 'custom_get_meta_sql');
此過濾器應位於WordPress主題的functions.php文件中。
首先你爲什麼使用INNER JOINs？ 那是什麼ORDER meta_value + 0？ 爲什麼你爲同一個meta_key檢查做3個OR？ – Svetoslav
該查詢由WP_Query生成。每個meta_key有3個ORS，因爲它會在每個元素中檢查不同的範圍/值。 –
我認爲給ORDER BY加上+0，它會「強制」mysql使用該值作爲數字，而不是文本。 –