Re-using statements with open ResultSet

Question

Hi,
Question about re-using connections while keeping a result set open - basically I am trying to do:
Connection conn = dataSource.getConnection();
Statement stmt = conn.createStatement();
if (stmt.execute(QUERY))
resultSet = stmt.getResultSet();
ArrayList userList = new ArrayList();
while (resultSet.next())
String str = resultSet.getString(1));
String otherStr = getString(str, conn));
where getString(str,conn) performs another query.
Is it recommended to use another connection for the call to the getString() method or is it safe to use the same connection? There won't be any other threads using the connection btw.
Thanks,
Johan

Answer 1

Unfortunately it isn't - i want to look up a list of
users (the first lookup) and then for each user, I
want to find out what groups they belong to. So the
sub-query is needed ... :(
I could do it in one query, but then I would have to
do a (sort of ugly) loop in the resultset while loop
...Are you a former VB programmer? Just curious...
I'll bet you'd be FAR better off doing a JOIN to bring back that data. If you have X users, you're saying that you're going to run a query like this once:
SELECT USER_ID FROM USERS WHERE SOME_ATTRIBUTE = y;Then you're going to loop over all the USER_IDs you get back and run another query like this, once per user:
SELECT GROUP_ID FROM GROUPS WHERE USER_ID = this_user_idwhere this_user_id is the current USER_ID value in your loop.
That means you're going to have X+1 network roundtrips. Network calls are the slowest thing you can possibly do.
Instead of doing that, someone who really knew SQL would write this:
SELECT GROUP_ID
FROM GROUPS, USERS
WHERE
GROUPS.USER_ID = this_user_id AND
GROUPS.USER_ID = USERS.USER_IDThat'll mean ONE network roundtrip - MUCH faster. It's called a JOIN, in case you didn't know.
The loop over the ResultSet will be no uglier than what you'll do to accomplish the JOIN in your own code. I'll bet it's cleaner. AND it'll do it in 1/(X+1) the time, because you'll only do 1 network roundtrip instead of (X+1).
Doing the JOIN in your code is the most foolish thing you can possibly do. You're saying that you can optimize the query better than the guy who wrote the SQL engine and optimizer for your database. I highly doubt it. JMO - MOD