MySQL - Ignore WHERE condition if key/value pair doesn't exist - php

Question

In a Wordpress order based system I am selecting people going to an event on a certain date and location.
I also need to see if there are any order notes existing for any matching orders, which I do by selecting the meta_value where the meta_key ="_wc_acof_2".
The problem is when I add the condition to my WHERE clause the code stops returning records where that meta key/value pair doesn't exist (i.e. there are no order notes). Whereas I still need to select those records just return null or similar for the order notes.
The problem line in the WHERE clause is:
AND jn_postmeta_guestnotes.meta_key = "_wc_acof_2"
In my head I would like to write that line similar to:
AND (jn_postmeta_guestnotes.meta_key = "_wc_acof_2" OR 'there is no matching meta_key so just ignore this condition and return the record anyway')
The full query:
SELECT
CONCAT_WS(" ",wp_postmeta.meta_value,jn_postmeta_lastname.meta_value) AS Name,
wp_woocommerce_order_itemmeta.meta_value AS Adults,
jn_postmeta_guestnotes.meta_value AS Notes
FROM
wp_postmeta
LEFT JOIN
wp_postmeta AS jn_postmeta_lastname ON wp_postmeta.post_id = jn_postmeta_lastname.post_id
LEFT JOIN
wp_postmeta AS jn_postmeta_guestnotes ON wp_postmeta.post_id = jn_postmeta_guestnotes.post_id
LEFT JOIN
wp_posts ON wp_postmeta.post_id = wp_posts.ID
LEFT JOIN
wp_woocommerce_order_items ON wp_woocommerce_order_items.order_id = wp_posts.ID
LEFT JOIN
wp_woocommerce_order_itemmeta ON wp_woocommerce_order_itemmeta.order_item_id = wp_woocommerce_order_items.order_item_id
LEFT JOIN
wp_woocommerce_order_itemmeta AS jn_woocommerce_order_itemmeta_location ON wp_woocommerce_order_itemmeta.order_item_id = jn_woocommerce_order_itemmeta_location.order_item_id
LEFT JOIN
wp_woocommerce_order_itemmeta AS jn_woocommerce_order_itemmeta_date ON wp_woocommerce_order_itemmeta.order_item_id = jn_woocommerce_order_itemmeta_date.order_item_id
WHERE
1 = 1
AND wp_postmeta.meta_key = "_billing_first_name"
AND jn_postmeta_lastname.meta_key = "_billing_last_name"
AND jn_postmeta_guestnotes.meta_key = "_wc_acof_2"
AND wp_woocommerce_order_itemmeta.meta_key = "Adults"
AND jn_woocommerce_order_itemmeta_location.meta_key = "Booking Type"
AND jn_woocommerce_order_itemmeta_location.meta_value LIKE "%'.$showlocation.'%"
AND jn_woocommerce_order_itemmeta_date.meta_key = "Booking Date"
AND (jn_woocommerce_order_itemmeta_date.meta_value = "'.$showdateformata.'" OR jn_woocommerce_order_itemmeta_date.meta_value = "'.$showdateformatb.'")
AND wp_posts.post_status = "wc-completed"
GROUP BY wp_posts.ID
Any advice much appreciated!

Answer 1

The answer is to put the extra bit in a sub-select like so:
(SELECT wp_postmeta.meta_value FROM wp_postmeta WHERE wp_postmeta.meta_key = "_wc_acof_2" AND wp_postmeta.post_id = wp_posts.ID) AS Notes

Answer 2

Just put all filtering condition on the ON so the left join work. On the WHERE will remove the nulls
.....
wp_woocommerce_order_itemmeta AS jn_woocommerce_order_itemmeta_date
ON wp_woocommerce_order_itemmeta.order_item_id = jn_woocommerce_order_itemmeta_date.order_item_id
AND 1 = 1
AND wp_postmeta.meta_key = "_billing_first_name"
AND jn_postmeta_lastname.meta_key = "_billing_last_name"
AND jn_postmeta_guestnotes.meta_key = "_wc_acof_2"
AND wp_woocommerce_order_itemmeta.meta_key = "Adults"
AND jn_woocommerce_order_itemmeta_location.meta_key = "Booking Type"
AND jn_woocommerce_order_itemmeta_location.meta_value LIKE "%'.$showlocation.'%"
AND jn_woocommerce_order_itemmeta_date.meta_key = "Booking Date"
AND
(
jn_woocommerce_order_itemmeta_date.meta_value = "'.$showdateformata.'"
OR
jn_woocommerce_order_itemmeta_date.meta_value = "'.$showdateformatb.'"
)
AND wp_posts.post_status = "wc-completed"