Privet!
Kakova raznica mezdu 2 sledujushimi zaprosami (odinakovymi logicheski) s tochki zrenija proizvoditel'nosti?

Zapros 1:
SELECT emp.fname,
emp.lname,
city.name city_name
FROM emp, city
WHERE emp.city_id = city.city_id;

Zapros 2:
SELECT fname,
lname,
(SELECT name
FROM city
WHERE city.city_id = emp.city_id) city_name
FROM emp;

Spasibo zaranee!