Re: Nest SQL queries and result sets?

From:
"Mo" <dmittleider@gmail.com>
Newsgroups:
comp.lang.java.help
Date:
28 Jul 2006 07:21:28 -0700
Message-ID:
<1154096487.984124.124920@s13g2000cwa.googlegroups.com>
These are two different databases. One is off an AS/400 mainframe and
the other is off a n AIX box running DB2 and eventually this will be
expanded for an Oracle database too.

Greg R. Broderick wrote:

"Mo" <dmittleider@gmail.com> wrote in news:1154037754.863609.184420
@s13g2000cwa.googlegroups.com:

I'm trying to use a while loop to loop through a result set, and inside
that results set call another query. Like....

database_conn1 = new DBConnection(url, user, pass);
database_conn2 = new DBConnection(url, user, pass);

ResultSet records_conn1 = database_conn1.executeQuery(sqlstatment01);

while (records_conn1.next()) {

          records1_conn.getString(1);

          ResultSet records_conn2 =
database_conn2.executeQuery(sqlstatment02);

          while (records_conn2.next()) {
                  records2_conn.getString(1);
          }

}

(I have try and catch around the while statements, just trying to keep
the code simple)

What happens is the outside result set gets the first record, the
inside record gets all of it's results and then it gives me a null
pointer exception. I'm not sure if it is because the inside result set
closes down everything or what. Is this even possible, or is there a
better way to do this?


I'd suggest collapsing the two queries into one query using a join on the two
tables and an ORDER BY clause to insure that one parent table's rows stay
together in the output results - it will save you multiple round trips to the
database at the cost of some denormalization.

Cheers
GRB

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