Woocommerce – SQL Display the parent title of the product with the child title

My first approach would be something like this. I can not test it cause I have no sample DB

Make your sample SQL a subquery of a new query (it has parent SKU)
Join with another subquery which contains parent SKU and the data you want.
The main Query selects the fields in the desired order.

SELECT baseSQL.title p_title, 
           parentSQL.title AS p_parent_title, -- second field in picture
           baseSQL.shortdesc AS p_shortdesc,
           baseSQL.longdesc AS p_longdesc,
           baseSQL.sku AS p_sku,
           baseSQL.parent_sku AS p_parent_sku,
           baseSQL.price AS p_price,
           baseSQL.img AS p_img,
           baseSQL.mall AS p_mall,
           baseSQL.product_categories AS p_categories
    FROM
      ( SELECT 
          wp_posts.post_title AS title,
          wp_posts.post_excerpt AS shortdesc,
          wp_posts.post_content AS longdesc,
          wp_postmeta1.meta_value AS sku,
          wp_postmeta6.meta_value AS parent_sku,
          wp_postmeta2.meta_value AS price,
          wp_posts1.guid AS img,
          wp_postmeta5.meta_value AS mall,
          GROUP_CONCAT( wp_terms.name ORDER BY wp_terms.name SEPARATOR ', ' ) AS product_categories
        FROM wp_posts
        LEFT JOIN wp_postmeta wp_postmeta1
          ON wp_postmeta1.post_id = wp_posts.ID
          AND wp_postmeta1.meta_key = '_sku'
        LEFT JOIN wp_postmeta wp_postmeta2
          ON wp_postmeta2.post_id = wp_posts.ID
          AND wp_postmeta2.meta_key = '_regular_price'
        LEFT JOIN wp_postmeta wp_postmeta3
          ON wp_postmeta3.post_id = wp_posts.ID
          AND wp_postmeta3.meta_key = '_thumbnail_id'
        LEFT JOIN wp_posts wp_posts1
          ON wp_posts1.ID = wp_postmeta3.meta_value
          AND wp_posts1.post_type = 'attachment'
        LEFT JOIN wp_postmeta wp_postmeta5
          ON wp_postmeta5.post_id = wp_posts.ID
          AND wp_postmeta5.meta_key = 'send'
        LEFT JOIN wp_postmeta wp_postmeta6
          ON wp_postmeta6.post_id = wp_posts.ID
          AND wp_postmeta6.meta_key = 'parent_plu'

        LEFT JOIN wp_term_relationships
          ON wp_term_relationships.object_id = wp_posts.ID
        LEFT JOIN wp_term_taxonomy
          ON wp_term_relationships.term_taxonomy_id = wp_term_taxonomy.term_taxonomy_id
          AND wp_term_taxonomy.taxonomy = 'product_cat'
        LEFT JOIN wp_terms
          ON wp_term_taxonomy.term_id = wp_terms.term_id
        WHERE wp_posts.post_type = 'product' AND ( wp_posts.post_status = 'publish'
        OR wp_posts.post_status = 'hidden') AND wp_postmeta5.meta_value = 'yes'
        GROUP BY wp_posts.ID
        ORDER BY sku ASC
      ) baseSQL

    LEFT JOIN
      (
        SELECT 
          wp_posts.post_title AS title,
          wp_postmeta1.meta_value AS sku
        FROM wp_posts
        LEFT JOIN wp_postmeta wp_postmeta1
          ON wp_postmeta1.post_id = wp_posts.ID
          AND wp_postmeta1.meta_key = '_sku'
      ) parentSQL

    ON baseSQL.parent_sku = parentSQL.sku 
    AND baseSQL.parent_sku > 0
    GROUP BY baseSQL.sku

Check the performance of this, maybe moving grouping and ordering outside will become in a better performance.

I don’t propose to make a subquery in a nested JOIN within original LEFT JOINS because I cannot test it and from here and now, I can’t image how would react this “cross joining” with postmeta1 and postmeta6.

I recommend to implement some trigger and have sku and parent_sku fields in table wp_posts and you could do simple subquery with the table itself.
In mySQL there is no hierarchical queries (until I know mySQL) like in Oracle, but maybe this helps to improve your query.
It’s up to you.

Sorry If this don’t work on copy/paste, It’s just an approach.

Edited with final functional SQL