how to navigate in self loop tables? - sql

Question

Consider the following table
create table EMPLOYEE
(
empno NUMBER not null,
ename VARCHAR2(100),
salary NUMBER,
hiredate DATE,
manager NUMBER
);
alter table EMPLOYEE add constraint PK_EMP primary key (EMPNO);
alter table EMPLOYEE
add constraint FK_MGR foreign key (MANAGER)
references EMPLOYEE (EMPNO);
which is a self looped table i.e. every employee has a manager, except for the root.
I want to run the following query on this table:
find all the employees having more salary than their managers?
P.S.
There is only one root in the structure
consider the following query
SELECT LPAD(emp.ename, (LEVEL-1)*5 + LENGTH(emp.ename), ' ') AS "Hierarchy"
FROM employee emp
START WITH emp.manager IS NULL
CONNECT BY manager = PRIOR empno;
the result would be something like this:
Alice
Alex
Abbey
Sarah
Jack
Bill
Jacob
Valencia
Bob
Babak
...
I made the following query
SELECT LPAD(emp.ename, (LEVEL-1)*5 + LENGTH(emp.ename), ' ') AS "Hierarchy"
FROM employee emp
START WITH empno IN (SELECT empno FROM employee)
CONNECT BY PRIOR manager = empno;
which makes a subtree for every employee in the employee table from bottom to top, but I don't know how to navigate through to get to the desired result!

Answer 1

Here is one way to do it
with fullemployee (empno, ename, salary, key)
as
(
select A.empno, A.ename, A.salary, A.empno || '.' from
employee A
where A.manager is null
union all
select C.empno, C.ename, C.salary, D.key || '.' || C.empno from
employee C
inner join fullemployee D on C.manager = D.empno
)
select E.ename, F.ename as manager from fullemployee E
inner join fullemployee F on E.key like F.key || '%' and E.key <> F.key
where E.salary > F.salary
or equivalently
with fullemployee (empno, ename, salary, key)
as
(
SELECT empno, ename, salary, SYS_CONNECT_BY_PATH(empno, '.') || '.'
FROM employee
START WITH manager is null
CONNECT BY PRIOR empno = manager
)
select E.ename, F.ename as manager from fullemployee E
inner join fullemployee F on E.key like F.key || '%' and E.key <> F.key
where E.salary > F.salary
SQL Fiddle - http://sqlfiddle.com/#!4/37f4ae/35

Answer 2

This should do the work. Remove that or condition if you don't want the 'root' in your list.
select e.empno, e.ename, e.salary from employee e
inner join employee mgr on mgr.empno = e.manager
where e.salary > mgr.salary
or (e.manager = mgr.empno)