SELECT 
  storefronts.* 
FROM 
  cscart_storefronts AS storefronts 
WHERE 
  1 = 1 
  AND storefronts.is_default IN ('Y') 
GROUP BY 
  storefronts.storefront_id 
ORDER BY 
  storefronts.is_default desc

Query time 0.00017

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE storefronts system 1

Result

storefront_id url redirect_customer is_default status access_key name theme_name is_accessible_for_authorized_customers_only
1 cs-cart.pixy.pro N Y N CS-Cart bright_theme N