ปัญหา Join Table 2 ตาราง หาค่าที่ไม่มีในอีก table 1 ทำไงดีครับ รบกวนหน่อย

select a.id, b.id from a left join b on a.id=b.id where b.id is null 

select a.id, b.id from a right join b on a.id=b.id where a.id is null 

select a.id, b.id from a left join b on a.id=b.id where b.id is null 
union
select a.id, b.id from a right join b on a.id=b.id where a.id is null 

SELECT * FROM categories left join product_material on categories.categories_id=product_material.material_cid 
WHERE product_material.material_cid is null

SELECT * FROM categories left join product_material on categories.categories_id=product_material.material_cid 
WHERE product_material.material_cid is null and product_material.material_pid='196'

SELECT DISTINCT
	categories.categories_id,
	categories.categories_name
FROM 
	categories INNER JOIN product_material ON categories.categories_id=product_material.material_cid 
WHERE
	product_material.material_pid=196

select b.* from product_material b 
left join categories a on a.category_id=b.material_cid
where b.material_pid=196 and a.category_id is null

select a.* from categories 
left join product_material b on a.category_id=b.material_cid and b.material_pid=196
where b.material_pid is null