WPDB query what is the cleanest method for a double query? - sql

Question

I am curious as to how best achieve this.
wpdb query 1:
$results = $wpdb->get_results(
"SELECT *
FROM $table_name
WHERE user_id = '$userid';"
);
I then want to do another wpdb query on a separate table using $results->post_id in the WHERE part of the query such as:
$results2 = $wpdb->get_results(
"SELECT *
FROM $table_name2
WHERE user_id = '$results->post_id' && type = '$type';"
);
I am conscious that $results will be an array so I don't think the above will work directly and some sort of compound "for each" seems cumbersome.
What are my options please?
Update example based on Jarlh's comment
$userid = get_current_user_id();
global $wpdb;
$table_name = $wpdb->prefix . 'postmeta';
$table2_name = $wpdb->prefix . 'posts';
$rewards_results = $wpdb->get_results(
"SELECT *
FROM $table_name
WHERE post_id in ("SELECT user_id
FROM $table2_name
WHERE user_id = '$userid';")"
);
Update 2:
$userid = get_current_user_id();
global $wpdb;
$table_name = $wpdb->prefix . 'postmeta';
$table2_name = $wpdb->prefix . 'posts';
$results = $wpdb->get_results(
"SELECT *
FROM $table_name
WHERE ID in (SELECT user_id
FROM $table2_name
WHERE user_id = '$userid')"
);
//return $results;
foreach ($results as $row) {
echo "<td class='dash-2-td'>" . esc_html($row->logo_id) . "</td>";
echo "<td class='dash-2-td'>" . esc_html($row->belongs_to) . "</td>";
echo "</tr>";
}
This is producing no output.
I need to search $table_name->post_id for rows that match $table2_name->ID where user_id = $userid
Update 3: print_r is just showing array(), seems empty
$userid = get_current_user_id();
global $wpdb;
//$table_name = $wpdb->prefix . 'postmeta';
//$table2_name = $wpdb->prefix . 'posts';
$results = $wpdb->get_results(
"SELECT $wpdb->posts.*
FROM $wpdb->posts, $wpdb->postmeta
WHERE $wpdb->posts.ID = $wpdb->postmeta.post_id
AND $wpdb->posts.post_author = $userid
AND $wpdb->postmeta.plan = 3981
");
return $results;
I ended up using wp_query which I had not even considered as an option.

Answer 1

As a solution, you can use INNER JOIN. Also, I'd suggest you to use $wpdb->prepare for escaping values. Here is an example:
$sql = $wpdb->prepare( "SELECT a.*, b.col1, b.col2 FROM $table1 as a INNER JOIN $table2 as b ON a.user_id = b.user_id WHERE a.user_id = %d AND b.type = %s", $user_id, $type );
$entries = $wpdb->get_results( $sql, ARRAY_A );
Hope it helps.