SQL join without data loss - sql

Question

I want a select that naturally joins 2 tables. Afer joining table A with table B the new temporary table C doesn't contain the row of table A if the primary key of this row is not used in any rows of table B. I understand why that happens, but I want the row also in table C.
Example
select deptno, dname, loc, count(deptno) empcount, round(avg(sal),2) avgsal
from dept natural join emp
group by deptno, dname, loc
Result:
DEPTNO DNAME LOC EMPCOUNT AVGSAL
---------- -------------- ------------- ---------- ----------
20 RESEARCH DALLAS 5 2175
10 ACCOUNTING NEW YORK 3 2916.67
30 SALES CHICAGO 6 1566.67
What I want:
DEPTNO DNAME LOC EMPCOUNT AVGSAL
---------- -------------- ------------- ---------- ----------
20 RESEARCH DALLAS 5 2175
10 ACCOUNTING NEW YORK 3 2916.67
30 SALES CHICAGO 6 1566.67
40 OPERATIONS BOSTON 0 0
Table dept (A):
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING NEW YORK
20 RESEARCH DALLAS
30 SALES CHICAGO
40 OPERATIONS BOSTON
Table emp (B):
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- --------- ---------- ---------- ----------
7369 SMITH CLERK 7902 17-DEC-80 800 20
7499 ALLEN SALESMAN 7698 20-FEB-81 1600 300 30
7521 WARD SALESMAN 7698 22-FEB-81 1250 500 30
7566 JONES MANAGER 7839 02-APR-81 2975 20
7654 MARTIN SALESMAN 7698 28-SEP-81 1250 1400 30
7698 BLAKE MANAGER 7839 01-MAY-81 2850 30
7782 CLARK MANAGER 7839 09-JUN-81 2450 10
7788 SCOTT ANALYST 7566 19-APR-87 3000 20
7839 KING PRESIDENT 17-NOV-81 5000 10
7844 TURNER SALESMAN 7698 08-SEP-81 1500 0 30
7876 ADAMS CLERK 7788 23-MAY-87 1100 20
7900 JAMES CLERK 7698 03-DEC-81 950 30
7902 FORD ANALYST 7566 03-DEC-81 3000 20
7934 MILLER CLERK 7782 23-JAN-82 1300 10

Answer 1

select deptno, dname, loc, count(deptno) empcount, round(avg(sal),2) avgsal
from dept
LEFT join emp
group by deptno, dname, loc
Is this what you are looking at? Check the output...

Answer 2

According to http://docs.oracle.com/javadb/10.8.3.0/ref/rrefsqljnaturaljoin.html you can do an outer natural join like so:
The following example is similar to the one above, but it also preserves
unmatched rows from the first (left) table:
SELECT * FROM COUNTRIES NATURAL LEFT JOIN CITIES
So you would do:
select deptno, dname, loc, count(deptno) empcount, round(avg(sal),2) avgsal
from dept natural left join emp
group by deptno, dname, loc

Answer 3

Use left join instead fo natural join.
select deptno, dname, loc, count(deptno) empcount, round(coalesce(avg(sal), 0),2) avgsal
from dept left join emp
group by deptno, dname, loc

Answer 4

Thanks a lot, it was the outer join I was looking for.
So here's the sql command that deliveres the result I was looking for:
SQL99-Syntax:
select deptno, dname, loc, nvl(ecount,0) empcount, nvl(round(avg(sal),2),0) avgsal
from dept left join emp using(deptno)
left join (select deptno, count(deptno) ecount
from emp
group by deptno) using(deptno)
group by deptno, dname, loc, ecount
Standard SQL-Syntax:
select d.deptno, d.dname, d.loc, nvl(n.ecount,0) empcount, nvl(round(avg(e.sal),2),0) avgsal
from dept d, emp e, (select deptno, count(deptno) ecount
from emp
group by deptno) n
where d.deptno = e.deptno (+)
and n.deptno (+) = e.deptno
group by d.deptno, d.dname, d.loc, n.ecount
The column empcount is 0 if there are no employees in the department. In the other solutions it was 1 because there was one row for each department after the outer join in the temporary table.