# find promotion's products with promotion_id = 2
# if product ids result is 2,7
select product_id from spree_product_promotion_rules 
where promotion_rule_id=(select id from spree_promotion_rules where type='Spree::Promotion::Rules::Product' and promotion_id=2)

# find the promotion product's quantity if order_id = 3
select distinct(spree_line_items.variant_id), spree_line_items.quantity from spree_product_promotion_rules
left join spree_line_items on spree_product_promotion_rules.product_id = spree_line_items.variant_id
where spree_product_promotion_rules.product_id in (2,7) and spree_line_items.order_id=3