SQL query - get a featured image's alt / alternative text

I am writing some SQL queries to get post data out of a database for certain posts (so WP functions are not an option). I am trying to get post IDs, post URLs, post featured image URLs and associated alt text for the featured images. Alt text is held in the postmeta table with the meta_key '_wp_attachment_image_alt'.

The query below works for everything except alt text. I am confident I need to use a left join because I want all posts returned regardless of whether they have featured images. My query however is returning null values for alt text for images I have confirmed have alt text.

SELECT 
    wp_posts.id as Post ID,
    wp_posts.guid as Post URL,
    (SELECT wp_posts.id
        FROM   wp_posts
        WHERE  wp_posts.id = pm13.meta_value) AS Featured Image ID,
    
    (SELECT wp_posts.guid
        FROM   wp_posts
        WHERE  wp_posts.id = pm13.meta_value) AS Featured Image URL,
    
    (SELECT pm14.meta_value
        FROM wp_postmeta
        WHERE  wp_posts.id = pm14.meta_value
        ) as Featured Image Alt Text

    FROM   wp_posts
    
    LEFT JOIN wp_postmeta pm13
        ON (
            pm13.post_id = wp_posts.ID  AND
            pm13.meta_key    = '_thumbnail_id'
        )

    LEFT JOIN wp_postmeta pm14
        ON (
            pm14.post_id = wp_posts.ID  AND
            pm14.meta_key    = '_wp_attachment_image_alt'
        )
    
    WHERE  wp_posts.post_status = publish
           AND wp_posts.post_type = post
    
    
    ORDER  BY wp_posts.post_date DESC