MySQL

Question

在基于 Wordpress 订单的系统中，我 select 让人们在特定日期和地点参加活动。

我还需要查看是否存在任何匹配订单的 订单备注，我通过 selecting meta_value 来做到这一点meta_key ="_wc_acof_2"。

问题是当我将条件添加到我的 WHERE 子句时，代码停止 returning 记录，其中元 key/value 对不存在（即没有订单注释）。而我仍然需要 select 这些记录只是 return null 或类似的订单备注。

WHERE 子句中的问题行是：

AND jn_postmeta_guestnotes.meta_key = "_wc_acof_2"

在我的脑海里，我想写下类似于：

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')

完整查询：

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

非常感谢任何建议！

Answer 1

答案是将额外的位放在子select中，如下所示：

(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

只需将所有筛选条件放在 ON 上，以便左连接起作用。在 WHERE 将删除空值

.....
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"

MySQL - 如果 key/value 对不存在则忽略 WHERE 条件

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

php

wordpress