--10 SQL statements, set operations

For multiple select statements merged results

• union and set deduplication
• and not re-set union all
• intersect intersection
• minus difference set

union

The combined set A and set B, but a set of two repeated portion is removed, are sorted

select deptno,ename from emp where deptno in (20,30)
 union
select deptno,ename from emp where deptno in (20,10);

DEPTNO ENAME
---------- ----------
10 CLARK
10 KING
10 MILLER
20 ADAMS
20 FORD
20 JONES
20 SCOTT
20 SMITH
30 ALLEN
30 BLAKE
30 JAMES
30 MARTIN
30 TURNER
30 WARD

 

union all

The combined set A and set B, not heavy, not ordering

select deptno,ename from emp where deptno in (20,30)
 union all
select deptno,ename from emp where deptno in (20,10);


DEPTNO ENAME
---------- ----------
20 SMITH
30 ALLEN
30 WARD
20 JONES
30 MARTIN
30 BLAKE
20 SCOTT
30 TURNER
20 ADAMS
30 JAMES
20 FORD
20 SMITH
20 JONES
10 CLARK
20 SCOTT
10 KING
20 ADAMS
20 FORD
10 MILLER

19 rows selected.

intersect

The intersection of two sets of portions, and to re-sort

select deptno,ename from emp where deptno in (20,30)
 intersect
select deptno,ename from emp where deptno in (20,10);

DEPTNO ENAME
---------- ----------
20 ADAMS
20 FORD
20 JONES
20 SCOTT
20 SMITH

minus

Taking the difference of the set of the two sets, the set A is present, it does not exist in the set of data B (B taken in the aggregate data set A does not exist), deduplication

select deptno,ename from emp where deptno in (20,30)
 minus
select deptno,ename from emp where deptno in (20,10);

DEPTNO ENAME
---------- ----------
30 ALLEN
30 BLAKE
30 JAMES
30 MARTIN
30 TURNER
30 WARD

6 rows selected.