Conditional testing in Oracle SQL - sql

Question

I am trying to write query on a tables which query record based on some condition plus I need one column as status which should checking matching record on another table and set value based on that test.
For example, we have these two tables:
| USER_ID | FIRST_NAME | LAST_NAME | CURR_STATUS |
--------------------------------------------------
| 1234567 | ABC | DEF | ACTIVE |
| 8910111 | GHI | JKL | INACTIVE |
| 2131415 | MNO | PQR | INACTIVE |
| 1617181 | STU | VWX | ACTIVE |
| 9202122 | YZA | BCD | ACTIVE |
--------------------------------------------------
Table: USER
| USER_ID | DOC_NAME |
---------------------
| 1234567 | EFG.TXT |
| 1617181 | HIJ.PDF |
----------------------
Table: USER_DOC
> select first_name, last_name, curr_status
//TODO some sql code for HAS_DOC logic
from USER
where CURR_STATUS = 'ACTIVE';
| FIRST_NAME | LAST_NAME | CURR_STATUS | HAS_DOC |
--------------------------------------------------
| ABC | DEF | ACTIVE | YES |
| STU | VWX | ACTIVE | YES |
| YZA | BCD | ACTIVE | NO |
--------------------------------------------------
Result
Right now I am doing this in Java code with two separate SQL calls:
First to get the all record matching record from USER table.
Then calling second query in the for loop
select user_id from user_doc from user_id = :userId;
I am trying to see if it is can be done with single SQL query and it is faster.
Any suggestion?

Answer 1

One possible solution is to use the EXISTS operator:
SELECT u.first_name, u.last_name, u.curr_status
FROM user u
WHERE u.curr_status = 'ACTIVE'
AND EXISTS (SELECT d.doc_name FROM user_doc d WHERE d.user_id = u.user_id);
If you need more information (say, a document count), you may also try
SELECT u.first_name, u.last_name, u.curr_status, COUNT(d.doc_name) AS num_documents
FROM user u LEFT JOIN user_doc d ON d.user_id = u.user_id
WHERE u.curr_status = 'ACTIVE'
GROUP BY u.first_name, u.last_name, u.curr_status
HAVING num_documents > 0;
One last alternative would be to use the IN operator
SELECT u.first_name, u.last_name, u.curr_status
FROM user u
WHERE u.curr_status = 'ACTIVE'
AND u.user_id IN (SELECT d.user_id FROM user_doc d);
EDIT The "HAS_DOC" attribute can be derived from the count, for example
-- Gets all users
SELECT u.first_name, u.last_name, u.curr_status, COUNT(d.doc_name) AS num_documents
FROM user u LEFT JOIN user_doc d ON d.user_id = u.user_id
WHERE u.curr_status = 'ACTIVE'
GROUP BY u.first_name, u.last_name, u.curr_status;
and in your Java code:
boolean hasDoc = resultSet.getInt("num_documents") > 0;

Answer 2

I recommend something like this. (EDIT: tested, and it works)
select u1.first_name, u1.last_name, u1.curr_status,
nvl2(u2.user_id, 'YES', 'NO') as has_doc
from USER u1
left join (select u.user_id
from USER u
where u.CURR_STATUS = 'ACTIVE'
and exists (
select null
from user_doc ud
where ud.user_id = u.user_id)
) u2 ON u1.user_id = u2.user_id
where u1.CURR_STATUS = 'ACTIVE';