MySQL Query within a Query

I don't know if this is the best way but it works. I did this:

$id is from the URL

$postId = DB::connection('mysql_second')->table('wp_postmeta')
            ->where('wp_postmeta.meta_value',  $id)->value('post_id');

I then placed that into my other query:

WHERE wp_posts.post_type = 'm6_projects' AND wp_posts.ID = :postId 

Would that be the best way?

Yes, your approach works well for the task you're trying to accomplish. By splitting the query and first fetching the post_id and then using it in the second query, you're effectively solving the problem. However, if you'd like to optimize it, you can combine both queries into a single query using a subquery. This can potentially improve performance by reducing the number of queries executed.

SELECT wp_posts.ID, wp_posts.post_content, wp_posts.post_title, 
       wp_posts.post_excerpt, wp_posts.post_name, 
       wp_postmeta.meta_key, wp_postmeta.meta_value
FROM wp_posts
RIGHT JOIN wp_postmeta ON wp_posts.ID = wp_postmeta.post_id
WHERE wp_posts.post_type = 'm6_projects'
  AND wp_posts.ID = (
        SELECT post_id 
        FROM wp_postmeta 
        WHERE wp_postmeta.meta_value = '5mt3807'
    )
  AND wp_postmeta.meta_value NOT LIKE 'field%'

@jsanwo64 Awesome, that works, thanks!! I had tried something similar but gave up:

WHERE wp_posts.post_type = 'm6_projects'
  AND  (
        SELECT post_id 
        FROM wp_postmeta 
        WHERE wp_postmeta.meta_value = '5mt3807' AS postID
    )

With a few variations but gave up. Thanks for the help and increasing my knowledge!