通过id wordpress获取数据

Problem

I have two different plugin tables and I want to get their value by sql. Problem is id where I cannot find connection which I can retrieve data.

Table 1 (bdt_mappress_posts)

postid = 2 and mapid = 3

Table 2 (bdt_mappress_maps)

mapid = 3 and obj = json

<? $postid = get_the_ID(); 
$results = $GLOBALS['wpdb']->get_results( 'SELECT obj FROM bdt_mappress_maps INNER JOIN bdt_mappress_posts WHERE bdt_mappress_maps.mapid = bdt_mappress_posts AND   bdt_mappress_posts.postid ='.$postid); print_r($results);
 ?>

$postid returns me id of the post. The sql returns me empty value, I know sql but not so strong. If someone can help me or give related post which I can find answer. Thanks beforehand!

assuming that the two table are related by mapid for both of the tables you should use a join with on condition

$results = $GLOBALS['wpdb']->get_results( 'SELECT mapid 
           FROM bdt_mappress_maps 
           INNER JOIN bdt_mappress_posts 
              on (bdt_mappress_maps.mapid = bdt_mappress_posts
                   AND   bdt_mappress_posts.id ='.$postid));

<? $postid = get_the_ID(); 
$results = $GLOBALS['wpdb']->get_results( 'SELECT obj FROM bdt_mappress_posts INNER JOIN bdt_mappress_maps WHERE bdt_mappress_posts.mapid = bdt_mappress_maps.mapid AND   bdt_mappress_posts.postid ='.$postid); print_r($results);
?>

Solve the problem

That should only changing the place the rule of the left sql