What are the product characteristic?
select * from product_characteristics
What are the names of the products that have only one product characteristic?
select t1.product_name from products as t1 join product_characteristics as t2 on t1.product_id = t2.product_id group by t1.product_id having count(*) = 1
Give their color descriptions and their product id instead.
select t1.product_id, t2.color_description from products as t1 join ref_colors as t2 on t1.color_code = t2.color_code join product_characteristics as t3 on t1.product_id = t3.product_id group by t1.product_id having count(*) = 1
How about for those that have least 2 product characteristics.
select t1.product_id, t2.color_description from products as t1 join ref_colors as t2 on t1.color_code = t2.color_code join product_characteristics as t3 on t1.product_id = t3.product_id group by t1.product_id having count(*) >= 2