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update ops$train05.emp 
set ename = 'SMITH'
where empno = 7902;

create public synonym
employee for train05.emp;

select ename from ops$train05.emp
where empno = 7902;

select * from emp, dept
where emp.deptno = dept.deptno
group by dept.deptno;

select dept.deptno from emp, dept
where emp.deptno = dept.deptno
group by dept.deptno;

select dept.deptno, count(*) from emp, dept
where emp.deptno (+) = dept.deptno
group by dept.deptno;

select dname 
from dept
where not exists
(select ename from emp
where emp.deptno = dept.deptno);