Union multiple table with different column for order by date - php

Question

I search a solution for do this req' SQL because this don't work, like_supplier table and like product table work correctly but when i add the table comments this don't work, i know haven't the same column in table comment but how i can do this correctly ? Thanks in advance.
SELECT DISTINCT *
FROM (
(SELECT DISTINCT lp.customer_id, lp.`date`, lp.`product_id`, lp.`classes`, Null as `comment`
FROM
`like_product` as lp,
`supplier_products` as sp
WHERE
sp.`product_id` = lp.`product_id`
AND sp.`supplier_id`=".$customer_id.")
UNION DISTINCT
(SELECT DISTINCT ls.`customer_id`,ls.`date`, Null as `product_id`, ls.`classes`, Null as `comment`
FROM
`like_supplier` as ls,
`supplier_products` as sp
WHERE
sp.`supplier_id`=".$customer_id."
AND sp.`product_id` = ls.`product_id`)
UNION DISTINCT
(SELECT com.`sender_id`, com.`date`, com.`product_id`, com.`classes`, com.`comment`
FROM `comments` as com)) as a
ORDER BY a.`date` desc

Answer 1

Try just to clarify all aliases and column names:
SELECT DISTINCT
a.id,
a.`date`,
a.product_id,
a.classes,
a.comment
FROM (
(SELECT DISTINCT
lp.customer_id as id,
lp.`date` as `date`,
lp.`product_id` as product_id,
lp.`classes` as classes,
Null as comment
FROM
`like_product` as lp
INNER JOIN
(SELECT *
FROM
`supplier_products`
WHERE
supplier_id=".$customer_id."
) as sp
ON
sp.`product_id` = lp.`product_id`
)
UNION DISTINCT
(SELECT DISTINCT
ls.`customer_id` as id,
ls.`date` as `date`,
Null as `product_id`,
ls.`classes`,
Null as `comment`
FROM
`like_supplier` as ls
INNER JOIN
(SELECT
*
FROM
`supplier_products`
WHERE
supplier_id=".$customer_id."
) as sp
ON sp.`product_id` = ls.`product_id`)
UNION DISTINCT
(SELECT
com.`sender_id` as id,
com.`date` as `date`,
com.`product_id` as product_id,
com.`classes` as classes,
com.`comment` as comment
FROM `comments` as com
)
) as a
ORDER BY a.`date` desc