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Top Ten Things You Need to Know About DB2 For z/OS
For DB2 DBAs and Developers
Join Craig Mullins and Datavail for this webinar as we:
- Count down the top ten most important things you need to know
- See what is most important for DBA, developers, and managers to understand about DB2 for z/OS
- Understand the hierarchy of DB2 performance tuning objectives
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Below is a preview of the webinar transcript.
Next, join predicates. If you’ve got a series of tables that are being joined together, and you should, this goes back to the first rule: let SQL do the work. Do the joins instead of multiple sequel statements that are then cobbled together in the program. When you’ve got multiple tables being joined in an SQL statement, be sure that you are providing appropriate joined predicates. What I mean by that, well if you have table A, B, and C, you should have wear clauses, or on clauses depending on how you close the joints, that connect table A to B, table B to C, or table C to A, C to B. There should be a path through all three of those tables or all X of those tables regarding the number of tables you have in the joint.
If you don’t have joint predicates, what you’re doing is causing DB2 to do a Cartesian product. A Cartesian product says, “Take all the rows in this table and join them to all the row in that table.” It’s going to take a lot of resources to do that and probably give you the wrong results. Whatever you’ve got joined, go back, check you got passed you where or on clauses.
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