看看meta_query_find_compatible_table_alias 中定义的筛选器wp-includes/class-wp-meta-query.php. 此筛选器的文档：

/**
 * Filters the table alias identified as compatible with the current clause.
 *
 * @since 4.1.0
 *
 * @param string|bool $alias        Table alias, or false if none was found.
 * @param array       $clause       First-order query clause.
 * @param array       $parent_query Parent of $clause.
 * @param object      $this         WP_Meta_Query object.
 */
return apply_filters( \'meta_query_find_compatible_table_alias\', $alias, $clause, $parent_query, $this );

// Reuse the same alias for the abc_type meta key.
function pets_modify_meta_query( $alias, $meta_query ) {
    if ( \'abc_type\' === $meta_query[\'key\'] ) {
        return \'mt1\';
    }

    return $alias;
}

// Filter the query.
add_filter( \'meta_query_find_compatible_table_alias\', \'pets_modify_meta_query\', 10, 2 );

$args = array(
    \'meta_query\' => array(
        \'relation\' => \'AND\',
        array(
            \'key\' => \'abc_type\',
            \'value\' => array(\'puppy\', \'kitten\'),
            \'compare\' => \'IN\',
        ),
        array(
            \'relation\' => \'OR\',
            array(
                \'relation\' => \'AND\',
                array(
                    \'key\' => \'abc_type\',
                    \'value\' => \'puppy\',
                    \'compare\' => \'=\',
                ),
                array(
                    \'key\' => \'abc_color\',
                    \'value\' => \'pink\',
                    \'compare\' => \'=\',
                ),
            ),
            array(
                \'relation\' => \'AND\',
                array(
                    \'key\' => \'abc_type\',
                    \'value\' => \'kitten\',
                    \'compare\' => \'=\',
                ),
                array(
                    \'key\' => \'abc_size\',
                    \'value\' => \'large\',
                    \'compare\' => \'=\',
                ),
            ),
        ),
    )
);

$q = new WP_Query($args);
echo \'<pre>\', print_r($q->request, true); die;

SELECT SQL_CALC_FOUND_ROWS
    wp_posts.ID
FROM wp_posts
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 )
WHERE
    1=1
AND
(
    ( mt1.meta_key = \'abc_type\' AND mt1.meta_value IN (\'puppy\',\'kitten\') )
    AND
    (
        (
            ( mt1.meta_key = \'abc_type\' AND mt1.meta_value = \'puppy\' )
            AND
            ( wp_postmeta.meta_key = \'abc_color\' AND wp_postmeta.meta_value = \'pink\' )
        )
        OR
        (
            ( mt1.meta_key = \'abc_type\' AND mt1.meta_value = \'kitten\' )
            AND
            ( mt1.meta_key = \'abc_size\' AND mt1.meta_value = \'large\' )
        )
    )
)
AND
    wp_posts.post_type = \'post\'
AND (
    wp_posts.post_status = \'publish\'
    OR
    wp_posts.post_status = \'future\'
    OR
    wp_posts.post_status = \'draft\'
    OR wp_posts.post_status = \'pending\'
)
GROUP BY wp_posts.ID ORDER BY wp_posts.post_date DESC LIMIT 0, 10

您可以使用posts_where 和posts_join 用于修改查询的筛选器。这不是很优雅，但你应该能够搞乱这两个过滤器，这样你的sql就更优化了。这是一种蛮力，但我在WP\\u查询类中找不到更好的方法。但这并不是说没有。

//* Make sure to not suppress filters
$args = array(
  \'suppress_filters\' => false,
  //* rest of args unchanged
);

add_filter( \'posts_where\', function( $sql ) {
  $sql = str_replace(
    "( mt1.meta_key = \'abc_type\' AND mt1.meta_value = \'puppy\' )",
    "( postmeta.meta_key = \'abc_type\' AND postmeta.meta_value = \'puppy\' )",
    $sql
  );

  $sql = str_replace(
    "( mt3.meta_key = \'abc_type\' AND mt3.meta_value = \'kitten\' )",
    "( postmeta.meta_key = \'abc_type\' AND postmeta.meta_value = \'kitten\' )",
    $sql
  );

  $sql = str_replace( [ \'mt2\', \'mt4\' ], [ \'mt1\', \'mt2\' ], $sql );
  return $sql;
});

add_filter( \'posts_join\', function( $sql ) {
  $sql = str_replace(
    " INNER JOIN wp_postmeta AS mt4 ON ( wp_posts.ID = mt4.post_id )",
    "",
    $sql
  );
  $sql = str_replace(
    " INNER JOIN wp_postmeta AS mt3 ON ( wp_posts.ID = mt3.post_id )",
    "",
    $sql
  );
  return $sql;
});

您可以通过删除第一个元查询来优化查询，因为它是冗余的，如下所示：

$args = array(
    \'meta_query\' => array(
        \'relation\' => \'OR\',
        array(
            \'relation\' => \'AND\',
            array(
                \'key\' => \'abc_type\',
                \'value\' => \'puppy\',
                \'compare\' => \'=\',
            ),
            array(
                \'key\' => \'abc_color\',
                \'value\' => \'pink\',
                \'compare\' => \'=\',
            ),
        ),
        array(
            \'relation\' => \'AND\',
            array(
                \'key\' => \'abc_type\',
                \'value\' => \'kitten\',
                \'compare\' => \'=\',
            ),
            array(
                \'key\' => \'abc_size\',
                \'value\' => \'large\',
                \'compare\' => \'=\',
            ),
        ),
    ),
);
get_posts($args);

至于优化WordPress的内部MySQL查询，我认为您应该远离这一点，因为您可能会暴露出可能的副作用。您最好依赖缓存查询的事实，并在（更大的）数据集上进行更多的PHP处理。我相信这将带来更好的总体性能，因为瓶颈不在于从数据库中提取的数据量，而在于收集数据的难度（查询的数量）。PHP通过数组的速度非常快。

因此，考虑到post meta被缓存，我认为这样的情况更快：

$args = array(
    \'meta_query\' => array( 
        array(
            \'key\' => \'abc_type\',
            \'value\' => array(\'puppy\', \'kitten\'),
            \'compare\' => \'IN\',
        ),
    ),
);

$final_posts = array();
foreach( $get_posts($args) as $post ) {
    if ( \'puppy\' === get_post_meta( $post->ID, \'abc_type\', true ) ) {
        if ( \'pink\' === get_post_meta( $post->ID, \'abc_color\', true ) ) {
            $final_posts[] = $post;
        }
    } else {
        // This is definitely a kitten
        if ( \'large\' === get_post_meta( $post->ID, \'abc_size\', true ) ) {
            $final_posts[] = $post;
        }
    }
}

我不是一个真正的数据库专家，但我曾经在电视上玩过一次。。。

这部分不是吗

SELECT posts.* FROM posts
INNER JOIN postmeta ON ( posts.ID = postmeta.post_id )
INNER JOIN postmeta AS mt1 ON ( posts.ID = mt1.post_id )
INNER JOIN postmeta AS mt2 ON ( posts.ID = mt2.post_id )

SELECT posts.* FROM posts
INNER JOIN postmeta ON (( posts.ID = postmeta.post_id ) and 
( posts.ID = mt1.post_id ) and
( posts.ID = mt2.post_id ))

只是一个想法。。。