SQL LEFT JOIN Subquery Alias
You didn't select post_id in the subquery. You have to select it in the subquery like this:
SELECT wp_woocommerce_order_items.order_id As No_CommandeFROM wp_woocommerce_order_itemsLEFT JOIN ( SELECT meta_value As Prenom, post_id -- <----- this FROM wp_postmeta WHERE meta_key = '_shipping_first_name' ) AS aON wp_woocommerce_order_items.order_id = a.post_idWHERE wp_woocommerce_order_items.order_id =2198
I recognize that the answer works and has been accepted but there is a much cleaner way to write that query. Tested on mysql and postgres.
SELECT wpoi.order_id As No_CommandeFROM wp_woocommerce_order_items AS wpoiLEFT JOIN wp_postmeta AS wpp ON wpoi.order_id = wpp.post_id AND wpp.meta_key = '_shipping_first_name'WHERE wpoi.order_id =2198