DB2 9 for z/OS introduces a new type of trigger: the INSTEAD OF trigger. The primary usage of INSTEAD OF triggers is to enable views that would not otherwise be updatable to support updates. Typically, a view that consists of multiple base tables cannot be updated. But with an INSTEAD OF trigger this problem can be surmounted. You can code an INSTEAD OF trigger to direct inserts, updates and deletes to the appropriate underlying tables of the view.With the INSTEAD OF trigger, your application code does not have to include complex algorithms to...
Tuesday, 29 May 2007
Thursday, 24 May 2007
LOB Enhancements [DB2 9 for z/OS]
Posted on 10:15 by Unknown
IBM focused their attention on improving DB2’s ability to store and manage LOB data in Version 9. As anyone who has tried to use LOBs in a previous version of DB2 knows, the usability limitations were troublesome. But with Version 9, IBM chips away at some of the more annoying LOB limitations. FETCHing LOBs Prior to Version 9, there were two methods you could deploy in your programs to fetch LOB data: Fetching data into a pre-allocated buffer Using a LOB locator to retrieve a handle on the data. Both methods have their issues. Fetching data into...
Monday, 21 May 2007
New OLAP Capabilities [DB2 9 for z/OS]
Posted on 12:56 by Unknown
DB2 9 for z/OS offers several new SQL improvements focused on improving OLAP functionality. The OLAP functions provide the ability to return ranking, row numbering, and existing aggregate function information as a scalar value in the result of a query. You can include OLAP specifications in an expression, in a select-list, or in the ORDER BY clause of a select-statement.The result to which the OLAP specification is applied is the result table of the innermost subselect that includes the OLAP specification. OK, at this point you might well be asking,...
Tuesday, 15 May 2007
Implicitly Hidden Columns [DB2 9 for z/OS]
Posted on 11:52 by Unknown
Another nice new feature deep in the bowels of DB2 9 for z/OS is the ability to hide columns from the SELECT * statement. As far back as anyone can remember the advice has been given to avoid using SELECT * in application programs. But I still see it every now and then.Now don't get me wrong, SELECT * is a nice shorthand when you are writing quick & dirty SQL using SPUFI or some other ad hoc SQL tool. But it does not belong in your application programs because a subsequent ALTER to add a column will cause the program to fail because there are...
Monday, 14 May 2007
Index on Expressions [DB2 9 for z/OS]
Posted on 14:05 by Unknown
DB2 9 for z/OS offers, for the first time, the ability to create an index on data that is not technically in the table. At this point, you may well be asking “What does that mean?” and “Why would I do that?” I’ll attempt to answer both of those questions.Basically, the neat new feature is an extension to the CREATE INDEX statement that lets you create an index on an expression. That begs the question of just what is an expression… Well, an expression can be as simple as a column reference, or it can be a built-in function invocation or even a more...
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