RE: Simple question: What is a hash join?

Hi Steve! I took it from my "Informix Unleashed" chapter, I hope this helps. [lb] Nested Loop Join ... .. [lb] Sort Merge Join... .. [lb] Hash joins are faster than the other two methods. A hash table is = typically created on the smaller table. Informix executes a hash = function on every row in the table, determining the hash bucket that = will hold the row. The rows in the buckets are not sorted. The hash = table is created in the virtual portion of the shared memory. When no = space is available in the virtual portion, then, it is partitioned out = to the dbspaces specified in the DBSPACETEMP environment variable or = configuration parameter. Mario Estrada=20 ----------------Reply Separator------------ ---------- From: Steve Kain[SMTP:skain@peapod.com] Sent: Viernes 9 de Mayo de 1997 04:29 PM To: informix-list@rmy.emory.edu Subject: Simple question: What is a hash join? Hi. I've been hearing about hash joins for quite a while now and I've always been kind of foggy on exactly what they are. As I understand it, the optimiser sometimes decides to do a hash join for a join between two tables, but I don't understand why. I'm guessing that if I knew what a hash join was, everything would be a lot clearer. Thanks, Steve Kain Peapod Inc.