MYSQL查询联接表

Question

这是我对WP数据库的查询。

$letters = $wpdb->get_col(
"SELECT DISTINCT LEFT(post_title,1) AS first_letter FROM $wpdb->posts
WHERE post_type = '$post_type' AND post_status = 'publish'
ORDER BY first_letter ASC"
);

这是一个婴儿的名字数据库，我想制作一个小部件以区分男性/女性，因此我需要像上面进行查询，但要获取仅具有某些postmeta信息的帖子，而这正是我要寻找的关键和价值。

按键-Spin2

价值-男性

由于它在另一个表中，如何将其添加到查询中？

谢谢！

Answer 1

您只需要使用INNER JOIN ：

SELECT DISTINCT LEFT(posts.post_title,1) AS first_letter 
FROM $wpdb->posts AS posts 
    INNER JOIN $wpdb->postmeta AS meta
        ON posts.ID = meta.post_id
WHERE posts.post_type = '$post_type' 
    AND posts.post_status = 'publish'
    AND meta.meta_key = 'spin2'
    AND meta.meta_value = 'Male'
ORDER BY first_letter ASC