ALL Clause with correlated sub queries

Question

I have two Tables. emp and dep. In Employee emp_id and Name where emp_id is pk. emp_id is referencing emp_id in Department where Dep has 3 columns emp_id Dep_no and Dep_name. In Department table emp_id is PK.
Say: Employee Has these data: 1|john and 2|Elen and 3|Ron AND Department Table Has 1|10|Accounts and 2|20|IT.
I give the following Query:
SELECT * from Employee E where emp_id = ALL (select emp_id from Department D where D.emp_id = E.emp_id);
I suppose i should get 1|john . But Im getting All rows of Employee. Why is that D.emp_id = E.emp_id has no effect. Cant seem to understand the query plan too

Answer 1

Hi,
ramki_noubang wrote:
im using oracle 10G XE.
consider two tables manager_emp and emp_rk: see the results below.
select * from manager_emp;
EMP_ID     LAST_NAME MANAGER_ID
1     ram     3
2     raj     3
3     govi     100
100     mgr     -Once again, post CREATE TABLE and INSERT statements for the sample data.
select * from emp_rk;
ID     NAME     DPNO     SAL
1     ram     10     1000
2     jon     10     2000
3     man     10     1500
4     dan     30     5000
select * from manager_emp m
where (emp_id,last_name) *= all* (select id,name from emp_rk e
where e.id = m.emp_id and e.name = m.last_name);
EMP_ID     LAST_NAME MANAGER_ID
1     ram     3
2     raj     3
3     govi     100
100     mgr     -
i should get only:
EMP_ID     LAST_NAME MANAGER_ID
1     ram     3Think about what's happening.
The main query is just
SELECT  *
FROM    manager_emp  m
WHERE   (emp_id, last_name)   = ALL (subquery)
;The subquery is correlated to the main query; that means for each row in manager_emp, the subquery will be run to see if the main WHERE condition is TRUE or not.
Think about what happens when it's deciding whether or not to include the row
EMP_ID     LAST_NAME      MANAGER_ID
2     raj            3It will run this sub-query:
...         SELECT  id
         ,         name
         FROM    emp_rk  e
         WHERE   e.id    = 2          -- because m.emp_id = 2
         AND     e.name  = 'raj'     -- because m.last_name = 'raj'The sub-query will find 0 rows, and so the main WHERE condition will be TRUE, because "x = ALL (subquery)" is defined as TRUE when the subquery produces no rows.
If you want just the 1 row you mentioned, then one way to get it is an uncorrelated sub-query, something like this:
SELECT  *
FROM    manager_emp
WHERE   (emp_id, last_name)   IN
         SELECT  id, name
         FROM    emp_rk
;Once again: forget about "= ALL". Everybody else has, and there's a good reason.