4 operations with Postrgres (select price from product_price where product_id=1)/(select price from comp_product_price where comp_product_id =1)

I'm holding the current price in the product price and the competitor product price at the comp_product_price. I would like to get the ratio of these. Above query gives the syntax error.
How can i handle the issue? Thanks.
Use a JOIN:
select pp.price / cpp.price
from product_price pp 
  join comp_product_price cpp on pp.product_id = cpp.comp_product_id
where pp.product_id=1