我为帖子设置了一个特殊的“position”元字段，可以在0到37之间。0被忽略，其他任何数字都可以是介于1和37之间（包括1和37）。但这当然意味着多个帖子可以有相同的数字。

现在我只想从这些副本中选择最新的条目，但是，我没有任何运气。以下是我为实现目前目标所采用的方法：

add_action( \'pre_get_posts\', \'foo_pre_get_posts\' );
function foo_pre_get_posts( $query ) {
    if (!is_admin() && is_home() && is_a( $query, \'WP_Query\' ) && $query->is_main_query() ) {
        $query->set( \'meta_key\', \'_position\' );
        $query->set( \'posts_per_page\', 37 );
        $query->set( \'meta_value\', \'0\' );
        $query->set( \'meta_compare\', \'>\' );
        $query->set( \'paged\', 1 );
    }
}

// order the stuff on meta value and then post date since pre_get_posts can\'t do it.
add_filter("posts_orderby", "foo_posts_orderby");
function foo_posts_orderby( $orderby) {
    if (!is_admin() && is_home()) {
        return "wp_postmeta.meta_value+0 ASC, wp_posts.post_date DESC";
    }
    return $orderby;
}

add_filter("posts_groupby", "foo_posts_groupby");
function foo_posts_groupby( $orderby) {
    if (!is_admin() && is_home()) {
        return "wp_posts.ID, wp_postmeta.meta_value";
    }
    return $orderby;
}

生成的SQL：

SELECT SQL_CALC_FOUND_ROWS  wp_posts.ID
FROM wp_posts
    INNER JOIN wp_postmeta ON (wp_posts.ID = wp_postmeta.post_id)
WHERE 1=1  AND
    wp_posts.post_type = \'post\' AND
    (wp_posts.post_status = \'publish\' OR wp_posts.post_status = \'private\') AND
    ( (
        wp_postmeta.meta_key = \'_position\' AND
        CAST(wp_postmeta.meta_value AS CHAR) > \'0\'
    ) )
GROUP BY wp_posts.ID, wp_postmeta.meta_value
ORDER BY wp_postmeta.meta_value+0 ASC, wp_posts.post_date DESC LIMIT 0, 31

我试过团员，但没用，我试过DISTINCT 直接在phpMyAdmin中（当然是复制生成的SQL），同样没有用。

我得到的结果是：

[ ID ] [ position ] [ date ]
  1         1         12/08/2012
  4         1         07/08/2012
  5         1         06/08/2012
  6         2         08/08/2012
  9         2         07/08/2012
  8         5         09/08/2012

注：这只是测试数据

如何使其仅根据位置选择第一个选项，例如：

[ ID ] [ position ] [ date ]
  1         1         12/08/2012
  6         2         08/08/2012
  8         5         09/08/2012

谢谢！

add_filter("posts_groupby", "foo_posts_groupby");
function foo_posts_groupby( $groupby) {
    if (!is_admin() && is_home()) {
        return "wp_postmeta.meta_value";
    }
    return $groupby;
}

SELECT SQL_CALC_FOUND_ROWS  wp_posts.ID
FROM wp_posts
    INNER JOIN wp_postmeta ON (wp_posts.ID = wp_postmeta.post_id)
WHERE 1=1  AND
    wp_posts.post_type = \'post\' AND
    (wp_posts.post_status = \'publish\' OR wp_posts.post_status = \'private\') AND
    ( (
        wp_postmeta.meta_key = \'_position\' AND
        CAST(wp_postmeta.meta_value AS CHAR) > \'0\'
    ) )
GROUP BY wp_postmeta.meta_value
ORDER BY wp_postmeta.meta_value+0 ASC, wp_posts.post_date DESC LIMIT 0, 31

SELECT SQL_CALC_FOUND_ROWS  wp_posts.ID
FROM wp_posts
    INNER JOIN wp_postmeta ON (wp_posts.ID = wp_postmeta.post_id)
WHERE 1=1  AND
    wp_posts.post_type = \'post\' AND
    (wp_posts.post_status = \'publish\' OR wp_posts.post_status = \'private\') AND
    ( (
        wp_postmeta.meta_key = \'_position\' AND
        CAST(wp_postmeta.meta_value AS CHAR) > \'0\'
    ) )
GROUP BY wp_posts.ID, wp_postmeta.meta_value
ORDER BY wp_postmeta.meta_value+0 ASC, wp_posts.post_date DESC LIMIT 0, 31

SELECT SQL_CALC_FOUND_ROWS  MIN(wp_posts.ID)
FROM wp_posts
    INNER JOIN wp_postmeta ON (wp_posts.ID = wp_postmeta.post_id)
WHERE 1=1  AND
    wp_posts.post_type = \'post\' AND
    (wp_posts.post_status = \'publish\' OR wp_posts.post_status = \'private\') AND
    ( (
        wp_postmeta.meta_key = \'_position\' AND
        CAST(wp_postmeta.meta_value AS CHAR) > \'0\'
    ) )
GROUP BY (wp_postmeta.meta_value+0);