There is no special SQL statements to calculate expressions. But you can use the "SELECT expression FROM DUAL" statement return the calculated value of an expression. "DUAL" is a dummy table in the server. The tutorial exercise below shows you some good examples:
SELECT 'Hello world!' FROM DUAL;
Hello world!
SELECT (1+2)*3/4 FROM DUAL;
2.2500
SELECT TRUE FROM DUAL;
1
SELECT TRUE AND FALSE FROM DUAL;
0
SELECT TIME(SYSDATE()) FROM DUAL;
21:30:26