UNION: Take the common record once( No Duplicate)

UNION ALL : Takes Duplicates also

Exampl : Say there is EMP having 14 reconds then...

select count(1) from (select ename from emp) returns 14

select count(1) from (select ename from emp union select ename from emp e1) returns 14

But

select count(1) from (select ename from emp union All select ename from emp e1)

returns 28.

UNION: Take the common record once( No Duplicate)

UNION ALL : Takes Duplicates also

Minus: Result of first query - result of second query

examle

select * from emp where rownum< 9;

minus

select * from emp where rownum<9;

this will display 9th row of emp

Intersect: common result of both query