What are the buying prices of the products with selling price < 500?
select typical_buying_price from products where typical_selling_price < 500
Show their names instead.
select product_name from products where typical_selling_price < 500
Of those, narrow down to ones with color "red" as well.
select t1.product_name from products as t1 join ref_colors as t2 on t1.color_code = t2.color_code where t1.typical_selling_price < 500 and t2.color_description = "red"
Remove the restriction of selling price.
select t1.product_name from products as t1 join ref_colors as t2 on t1.color_code = t2.color_code where t2.color_description = "red"
How many are there?
select count(*) from products as t1 join ref_colors as t2 on t1.color_code = t2.color_code where t2.color_description = "red"
Restrict also to those with characteristic named "slow" as well.
select count(*) from products as t1 join product_characteristics as t2 on t1.product_id = t2.product_id join characteristics as t3 on t2.characteristic_id = t3.characteristic_id join ref_colors as t4 on t1.color_code = t4.color_code where t4.color_description = "red" and t3.characteristic_name = "slow"