SQL Query Comparing Two varray() - sql

Question

I have a table of employees. One of the columns is a varray() that contains multiple room #'s for their office. I'm looking for a simple query that will compare each employee to see if they share an office.
SELECT E1.Name, E2.Name
FROM Employee E1
JOIN Employee E2
ON E1.Room = E2.Room;
Something like this doesn't work because the Room column is a varray. I just need one value in the first varray to match with another in the second. Is there an easy way of doing this?

Answer 1

Assuming you refer to Oracle, the query of your choice could be either
select
E1.name as employee_1, E2.name as employee_2,
R1.column_value as the_matching_room
from employee E1
cross join table(E1.rooms) R1
join employee E2
on E2.emp_id > E1.emp_id
join table(E2.rooms) R2
on R2.column_value = R1.column_value
;
or (somewhat more effective)
with rooms_unnested$ as (
select E.emp_id, E.name, R.column_value as room
from employee E
cross join table(E.rooms) R
)
select
E1.name as employee_1, E2.name as employee_2,
E1.room as the_matching_room
from rooms_unnested$ E1
join rooms_unnested$ E2
on E2.emp_id > E1.emp_id
and E2.room = E1.room
;
This one has the potential problem of doing the cartesian between employee tables first, unnesting the collections later:
-----------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost | Time |
-----------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1334324 | 5142484696 | 447202 | 00:00:18 |
| 1 | NESTED LOOPS | | 1334324 | 5142484696 | 447202 | 00:00:18 |
| 2 | NESTED LOOPS | | 16336 | 62926272 | 63 | 00:00:01 |
| 3 | NESTED LOOPS | | 2 | 7700 | 7 | 00:00:01 |
| 4 | TABLE ACCESS FULL | EMPLOYEE | 2 | 3850 | 3 | 00:00:01 |
| * 5 | TABLE ACCESS FULL | EMPLOYEE | 1 | 1925 | 2 | 00:00:01 |
| 6 | COLLECTION ITERATOR PICKLER FETCH | | 8168 | 16336 | 28 | 00:00:01 |
| * 7 | COLLECTION ITERATOR PICKLER FETCH | | 82 | 164 | 27 | 00:00:01 |
-----------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
------------------------------------------
* 5 - filter("E2"."EMP_ID">"E1"."EMP_ID")
* 7 - filter(VALUE(KOKBF$)=VALUE(KOKBF$))
With the assumption that your "rooms" varrays may contain duplicates, there's one more tweak to do - making each employee's rooms distinct, which leads us to the (hopefully) final query...
with rooms_unnested$ as (
select distinct
E.emp_id, E.name, R.column_value as room
from employee E
cross join table(E.rooms) R
)
select
E1.name as employee_1, E2.name as employee_2,
E1.room as the_matching_room
from rooms_unnested$ E1
join rooms_unnested$ E2
on E2.emp_id > E1.emp_id
and E2.room = E1.room
;
... which also happens to resolve the "issue" with cartesians by unnesting the "rooms" varray first (and only once!) and equi-hash-joining afterwards:
---------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost | Time |
---------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 120 | 65 | 00:00:01 |
| 1 | TEMP TABLE TRANSFORMATION | | | | | |
| 2 | LOAD AS SELECT (CURSOR DURATION MEMORY) | SYS_TEMP_0FD9D6699_11FF28DD | | | | |
| 3 | HASH UNIQUE | | 3 | 36 | 61 | 00:00:01 |
| 4 | NESTED LOOPS | | 16336 | 196032 | 59 | 00:00:01 |
| 5 | TABLE ACCESS FULL | EMPLOYEE | 2 | 20 | 3 | 00:00:01 |
| 6 | COLLECTION ITERATOR PICKLER FETCH | | 8168 | 16336 | 28 | 00:00:01 |
| * 7 | HASH JOIN | | 1 | 120 | 4 | 00:00:01 |
| 8 | VIEW | | 3 | 180 | 2 | 00:00:01 |
| 9 | TABLE ACCESS FULL | SYS_TEMP_0FD9D6699_11FF28DD | 3 | 36 | 2 | 00:00:01 |
| 10 | VIEW | | 3 | 180 | 2 | 00:00:01 |
| 11 | TABLE ACCESS FULL | SYS_TEMP_0FD9D6699_11FF28DD | 3 | 36 | 2 | 00:00:01 |
---------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
------------------------------------------
* 7 - access("E2"."ROOM"="E1"."ROOM")
* 7 - filter("E2"."EMP_ID">"E1"."EMP_ID")