In SELECT AVG (salary) FROM employees.. dont we need to add AS salary after AVG (salary) ?

Answer 1

No...
Coz we r not selecting the average of salaries as salary .....we want only the average of salaries as the result

Answer 2

it bassed on our needs if you want new name for the result so you use the AS to give the name for it

Answer 3

if U need to provide a new name for a column to be returned with data - so we use 'AS'