結局、友人が私の解決策を手伝ってくれました。これは、メタ情報を含むすべての投稿をCSVファイルにエクスポートするための彼の最後のSQLクエリでした。
SELECT DISTINCT
post_title
, post_content
,(SELECT meta_value FROM wp_postmeta WHERE wp_postmeta.meta_key = 'Asking Price (US\$)' AND wp_postmeta.post_id = wp_posts.ID) as "Asking Price (US\$)"
,(SELECT meta_value FROM wp_postmeta WHERE wp_postmeta.meta_key = 'Asking Price (ZAR)' AND wp_postmeta.post_id = wp_posts.ID) as "Asking Price (ZAR)"
,(SELECT meta_value FROM wp_postmeta WHERE wp_postmeta.meta_key = 'Author' AND wp_postmeta.post_id = wp_posts.ID) as Author
,(SELECT meta_value FROM wp_postmeta WHERE wp_postmeta.meta_key = 'Binding' AND wp_postmeta.post_id = wp_posts.ID) as Binding
,(SELECT meta_value FROM wp_postmeta WHERE wp_postmeta.meta_key = 'Book Condition' AND wp_postmeta.post_id = wp_posts.ID) as "Book Condition"
,(SELECT meta_value FROM wp_postmeta WHERE wp_postmeta.meta_key = 'Book Number' AND wp_postmeta.post_id = wp_posts.ID) as "Book Number"
,(SELECT meta_value FROM wp_postmeta WHERE wp_postmeta.meta_key = 'Book Type' AND wp_postmeta.post_id = wp_posts.ID) as "Book Type"
,(SELECT meta_value FROM wp_postmeta WHERE wp_postmeta.meta_key = 'Edition' AND wp_postmeta.post_id = wp_posts.ID) as Edition
,(SELECT meta_value FROM wp_postmeta WHERE wp_postmeta.meta_key = 'Illustrator' AND wp_postmeta.post_id = wp_posts.ID) as Illustrator
,(SELECT meta_value FROM wp_postmeta WHERE wp_postmeta.meta_key = 'Inscription' AND wp_postmeta.post_id = wp_posts.ID) as Inscription
,(SELECT meta_value FROM wp_postmeta WHERE wp_postmeta.meta_key = 'ISBN' AND wp_postmeta.post_id = wp_posts.ID) as ISBN
,(SELECT meta_value FROM wp_postmeta WHERE wp_postmeta.meta_key = 'Jacket Condition' AND wp_postmeta.post_id = wp_posts.ID) as "Jacket Condition"
,(SELECT meta_value FROM wp_postmeta WHERE wp_postmeta.meta_key = 'Location' AND wp_postmeta.post_id = wp_posts.ID) as Location
,(SELECT meta_value FROM wp_postmeta WHERE wp_postmeta.meta_key = 'Published Place' AND wp_postmeta.post_id = wp_posts.ID) as "Published Place"
,(SELECT meta_value FROM wp_postmeta WHERE wp_postmeta.meta_key = 'Published Year' AND wp_postmeta.post_id = wp_posts.ID) as "Published Year"
,(SELECT meta_value FROM wp_postmeta WHERE wp_postmeta.meta_key = 'Publisher' AND wp_postmeta.post_id = wp_posts.ID) as Publisher
,(SELECT meta_value FROM wp_postmeta WHERE wp_postmeta.meta_key = 'Size' AND wp_postmeta.post_id = wp_posts.ID) as Size
FROM wp_posts
WHERE post_type = 'post'
ORDER BY
post_title
, post_content
ご意見ありがとうございます!