Tag: Oracle

• TimesTen gets usually deployed in the Middle Tier – same location where the application runs
• TimesTen is persistent and can run as the only database on a system
• TimesTen persists to the disk over a background process
• TimesTen supports High Availability
• TimesTen can be used as cache between the application and the Oracle database
• TimesTen can be linked into applications directly – the calls to TimesTen happens over normal subroutine calls in the code which require no context switches on the system
• You can cache either a group of related tables or even a subset of specific rows
• TimesTen supports read-only and update able caches
• TimesTen supports “DynamicLoad” which loads the data from Oracle when you need it
• You can have as much read-only subscribers as you want
• TimesTen supports SQL and PL/SQL
• TimesTen is certified on all main application servers and OR-Mapping tools like Hibernate

In my last two posts I talked a little bit about bitmap indexes, how they work and why they lock. I also mentioned that they should be used for low cardinality but that there is no cut-and-dried answer about what low cardinality is. I’m not starting here to talk about cardinality on bitmap indexes, actually Richard Foote did a much better job on that so if you interested in that check out the following blog posts from him:

• Myth: Bitmap Indexes with high distinct columns (Blow Out)
• Myth: Bitmap Indexes with high distinct columns (Supermassive Black Hole)
• So what is a good cardinality estimate for a bitmap index column?

Last Wednesday I had the chance to visit an Oracle seminar at the Marriot hotel in New York City. I was really happy since it was already a long time ago when I last visited an Oracle event (except the Oracle User Group Meeting but that’s not Oracle itself). There were four tracks to join: Database developer, .NET developer, Java developer and APEX developer. All of them sounded interesting but as you had to bring your own laptop and install a specific image for each track I had to decide for one. Well it wasn’t to hard for me and I took the Database developer track with Hands-On on SQL Developer, SQL Developer Data Modeler, TimesTen and last but not least XML database. I have to say, that I was really excited about the sessions. I use SQL Developer and the Data Modeler part already quite a long time so there wasn’t much new for me but still something to learn (there is always something to learn!) The TimesTen and the XML database part was totally new to me and I was surprised what Oracle can already do with all the other products the own. Funniest thing was that I won a book of SQL Developer 2.1 which is brand-new and still wet from the press! 😉 This was because I was the first who finished all SQL Developer related hands-on – I wasn’t aware that I can win a prize for this, but hey, a book is always good! 🙂

So the best things out of this seminar were:

• SQL Developer can debug PL/SQL (not really new)
• SQL Developer can build, maintain and execute Unit tests for PL/SQL
• SQL Developer can connect to TimesTen since 1.6
• SQL Developer has a new Query Executor which makes executing stuff against different databases much more flexible
• TimesTen is really fast if you use it right (made selfwritten tests on my laptop bringing me 8.6 times more performance)

Well at the end here it’s time for some pics:

And here the prize I won:

How often have you been in a situation where you wanted to do an IF/ELSE in a SQL query. How often have you then written “SELECT … DECODE (expression, value, return, value, return, default return) FROM….” or even worse and selected the values and did then an IF/ELSE in PL/SQL?

The good thing in Oracle is that you can do a really IF/ELSE in the SQL query using the CASE expression. The documentation says following:

CASE expressions let you use IF … THEN … ELSE logic in SQL statements without having to invoke procedures. The syntax is:

CASE { simple_case_expression
     | searched_case_expression
     }
     [ else_clause ]
     END

Ok here first a short example of the “simple_case_expression”:

SQL> SELECT name,
2            CASE salery
3                 WHEN 1000 THEN ‘Low’
4                 WHEN 2000 THEN ‘Medium’
5                 WHEN 3000 THEN ‘Medium’
6                 ELSE ‘High’
7           END
8           FROM employee;

NAME                      CASESA
————————- ——
John                      Low
Andreas               Medium
Harry                    Medium
Mike                      High

So here you can see a simple IF/ELSIF/ELSE based on a column value. But what if you have some more complex logic like comparing two values with and AND. Well also that works in the “searched_case_expression”:

SQL> select name,
2             CASE
3                 WHEN salery = 1000 THEN ‘Low’
4                 WHEN salery = 2000 OR salery = 3000 THEN ‘Medium’
5                 ELSE ‘High’
6             END
7             FROM employee;

NAME                      CASEWH
————————- ——
John                        Low
Andreas                 Medium
Harry                      Medium
Mike                         High

Here you can see that I’m using  an OR clause like in the ELSIF. That also works with bind variables of course!

So this should help you in future when you have a select and you think of DECODE or PL/SQL IF/ELSE!