Select Query with Recursion - sql

Question

I have two tables containing employee names (TableB) and Employee hierarchy( TableA) (manager_id from TableA can be employee_id in the same table ).
TableA
UniqueId Employee_ID Manager_ID
1 101 102
2 102 103
3 103 104
4 105 106
5 106 null
TableB
Employee_ID Employee_Name
101 First
102 Second
103 Third
104 Fourth
105 Fifth
106 Sixth
and I need output as below :
Employee_ID Employee_Name Transferred
101 First True
102 Second True
103 Third True
105 Fifth False
106 Sixth False
The Transferred column for each employee is calculated as =
isTransferred(Employee_ID)
{
If(Manager_ID is null) return false;
If(Manager_ID is present as employee_id in table A)
{
return isTransferred(manager_ID)
}
else
{
return true;
}
}
Is there any way to get the result in one select statement?

Answer 1

You can use a Recursive CTE and then get the last level of "recursion" for each employee. Once you have that, you just check the manager_id of that last level to find out if it's transferred.
For example:
with
tablea as (
select 1 as uniqueId, 101 as employee_id, 102 as manager_id from dual union all
select 2 as uniqueId, 102 as employee_id, 103 as manager_id from dual union all
select 3 as uniqueId, 103 as employee_id, 104 as manager_id from dual union all
select 4 as uniqueId, 105 as employee_id, 106 as manager_id from dual union all
select 5 as uniqueId ,106 as employee_id, null from dual
),
tableb as (
select 101 as employee_id, 'first' as employee_name from dual union all
select 102 as employee_id, 'second' as employee_name from dual union all
select 103 as employee_id, 'third' as employee_name from dual union all
select 104 as employee_id, 'fourth' as employee_name from dual union all
select 105 as employee_id, 'fifth' as employee_name from dual union all
select 106 as employee_id, 'sixth' as employee_name from dual
),
n (employee_id, employee_name, lvl, manager_id) as (
select b.employee_id, b.employee_name, 1, a.manager_id
from tablea a
join tableb b on a.employee_id = b.employee_id
union all
select
n.employee_id, n.employee_name, lvl + 1, a.manager_id
from n
join tablea a on a.employee_id = n.manager_id
),
m (employee_id, max_lvl) as (
select employee_id, max(lvl) from n group by employee_id
)
select n.employee_id, n.employee_name,
case when n.manager_id is not null then 'True' else 'False' end as transferred
from n
join m on n.employee_id = m.employee_id and n.lvl = m.max_lvl
order by n.employee_id
Result:
EMPLOYEE_ID EMPLOYEE_NAME TRANSFERRED
----------- ------------- -----------
101 first True
102 second True
103 third True
105 fifth False
106 sixth False

Answer 2

You can do it with a single pass through the tree as follows:
Outer join the management chain to the employees
Find the employees with no manager by mapping the unique_id to an "impossible" value, e.g. -1
Use the results of this join to walk down the tree, starting with the rows where the manager is null
Get the value for the expression in step 2 for the root rows; if this is the "impossible" value, then transfer => true
Filter out the rows for the impossible value
Which gives something like:
with table_a ( UniqueId, Employee_ID, Manager_ID ) as (
select 1, 101, 102 from dual union all
select 2, 102, 103 from dual union all
select 3, 103, 104 from dual union all
select 4, 105, 106 from dual union all
select 5, 106, null from dual
), Table_b ( Employee_ID, Employee_Name ) as (
select 101, 'First' from dual union all
select 102, 'Second' from dual union all
select 103, 'Third' from dual union all
select 104, 'Fourth' from dual union all
select 105, 'Fifth' from dual union all
select 106, 'Sixth' from dual
), rws as (
select b.*, a.Manager_ID,
nvl ( a.UniqueId, -1 ) transfer
from table_b b
left join table_a a
on b.Employee_ID = a.Employee_ID
)
select r.*,
case connect_by_root transfer
when -1 then 'true'
else 'false'
end transferred
from rws r
where transfer > 0
start with manager_id is null
connect by manager_id = prior employee_id;
EMPLOYEE_ID EMPLOYEE_NAME MANAGER_ID TRANSFER TRANSFERRED
103 Third 104 3 true
102 Second 103 2 true
101 First 102 1 true
106 Sixth <null> 5 false
105 Fifth 106 4 false