EXCEPT and INTERSECT

Except - It returns data from left side query expression that is not in the data by right side query expression.
Ex.

A - data that is not in right side query result
B - data that is not in left side query result
C - data that is common in both results

Except returns A. 

Intersect - It returns data that is common in left and right side query expressions.
Intersect returns C.

Syntax -

{ <query_specification> | ( <query_expression> ) } 
{ EXCEPT | INTERSECT }
{ <query_specification> | ( <query_expression> ) }