Question

I know there's a lot of posts about this, but I just don't don't understand how to do this?

This is the code I'm using (no merging here):

SELECT coupon_code, order_id, youwp_woocommerce_order_itemmeta.meta_value, youwp_postmeta.meta_value  

FROM `youwp_woocommerce_order_items`, `youwp_woocommerce_order_itemmeta`, `youwp_postmeta`, `you_ambassador`  

WHERE you_ambassador.user_id = 1
AND youwp_woocommerce_order_items.order_item_name = you_ambassador.coupon_code
AND order_id = youwp_postmeta.post_id
AND youwp_woocommerce_order_items.order_item_id = youwp_woocommerce_order_itemmeta.order_item_id
AND youwp_woocommerce_order_itemmeta.meta_key = 'discount_amount'
AND (youwp_postmeta.meta_key = '_billing_first_name' OR youwp_postmeta.meta_key = '_billing_last_name')

Which gives me:

Query results

And I want to merge/combine the meta_value data "Kennet Leth" and "Sørensen" which is:

youwp_postmeta.meta_key = '_billing_first_name'
youwp_postmeta.meta_key = '_billing_last_name'

I found some answers to similar questions using STUFF or MAX and GROUP BY, but I just don't understand the syntax?

It's when the answers use selections like t1 and t2 or A and B (t1.value - t2.value or A.value = B.value) that I just don't get?
I've tried to change these solutions so they will fit my code, but just can't get it to work:

SELECT STUFF((SELECT ', ' + A.[Bank Account No] FROM tbl_Customer_Bank_Details A
Where A.[Customer ID]=B.[Customer ID] FOR XML PATH('')),1,1,'') As [Bank Accounts]
From tbl_Customer_Bank_Details B
Group By [Customer ID], [Customer Name]

or

SELECT Code,
   ( SELECT Name + ' '
       FROM Table1 t2
      WHERE t2.Code = t1.Code
      ORDER BY Name
        FOR XML PATH('') ) AS Name
  FROM Table1 t1
  GROUP BY Code ;

How do I put in my table and column values?

EDIT:
To clarify I'm trying to merge 2 rows/results from the column ´youwp_postmeta.meta_value´.
I get the results from specifying:

WHERE (youwp_postmeta.meta_key = '_billing_first_name'  
OR youwp_postmeta.meta_key = '_billing_last_name')
AND order_id = youwp_postmeta.post_id

so I get 2 rows for each order_id, one for _billing_first_name and one for _billing_first_name and these are the rows I want to merge/join.

Answer 1

Found a way to do it ;)

Just changed my SELECT string to include underqueries and CONCAT():

SELECT coupon_code, order_id, im.meta_value, 
CONCAT((SELECT pm.meta_value FROM `youwp_postmeta` AS pm WHERE pm.meta_key = 
'_billing_first_name' AND order_id = pm.post_id), ' ',
(SELECT pm.meta_value FROM `youwp_postmeta` AS pm WHERE pm.meta_key = 
'_billing_last_name' AND order_id = pm.post_id)) AS name

FROM 
`youwp_woocommerce_order_items` AS i,
`youwp_woocommerce_order_itemmeta` AS im,
`youwp_postmeta` AS pm,
`you_ambassador` AS a