12c

Something new in 12c: FETCH FIRST x ROWS

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In this post I want to show some example of using a new feature in 12c for selecting the first X number of records from the results set of a query.

See the bottom of this post for the background and some of the reasons for this post.

Before we had the 12c Database if we only wanted to see a subset or the initial set of records from the results of a query we could add something like the following to our query

AND ROWNUM <= 5;

The could use the pseudo column ROWNUM to restrict the number of records that would be displayed. This was particularly useful when the results many 10s, 100s, or millions of records. It allowed us to quickly see a subset and to see if the results where what we expected.

In my book (Predictive Analytics Using Oracle Data Miner) I had lots of examples of using ROWNUM.

What I wasn’t aware of when I was writing my book was that there was a new way of doing this in 12c. We now have something like the following:

FETCH FIRST x ROWS ONLY;

There is an example:

SELECT * FROM mining_data_build_v

FETCH FIRST 10 ROWS ONLY;

Fetch first 1

There are a number of different ways you can use the row limiting feature. Here is the syntax for it:

[ OFFSET offset { ROW | ROWS } ]

[ FETCH { FIRST | NEXT } [ { rowcount | percent PERCENT } ]

{ ROW | ROWS } { ONLY | WITH TIES } ]

In most cases you will probably use the number of rows. But there many be cases where you might what to use the PERCENT. In previous versions of the database you would have used SAMPLE to bring back a certain percentage of records.

select CUST_GENDER from mining_data_build_v

FETCH FIRST 2 PERCENT ROWS ONLY;

This will set the first 2 percent of the records.

You can also decide from what point in the result set you want the records to be displayed from. In the previous examples above the results displayed will befing with the first records. In the following example the results set will be processed to record 60 and then the first 5 records will be selected and displayed. This will be records 61, 62, 63, 64 and 65. So the first record processed will be the OFFSET record + 1.

select CUST_GENDER from mining_data_build_v

OFFSET 60 ROWS FETCH FIRST 5 ROWS ONLY;

Similar to the PERCENT example above you can use the OFFSET value, for example.

select CUST_GENDER from mining_data_build_v

OFFSET 60 ROWS FETCH FIRST 2 PERCENT ROWS ONLY;

This query will go to records 61 and return the next 2 percent of the records.

The background to this post

There are a number of reasons that I really love attending Oracle User Group conferences. One of the challenges I set myself is to go to presentations on topics that I think I know or know very well. I can list many, many reasons for this but there are 2 main points. The first is that you are getting someone elses perspective on the topic and hence you might learn something new or understand it better. The second is that you might actually learn something new, like some new command, parameter setting or something else like that.

At Oracle Open World recently I attended the EMEA 12 things about 12c set of presentations that Debra Lilly arranged during the User Group Forum on the Sunday. During these session Alex Nuijten gave an overview of some 12c new SQL features. One of these was the command FETCH FIRST x ROWS. This blog post illustrates some of the different ways of using this command.

Installing Oracle 12.1.0.2 on Windows 64bit

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The following steps are what I did for installing 12.1.0.2 on Windows.

1. Download the Oracle installation ZIP files from the Oracle Downloads page.

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2. Unzip the two 12c downloads files into the same directory.

3. Go to the newly created directory (it is probably called ‘database’) and you will find a file called setup.exe. Double click on this file.

DB Install 1

After a couple of seconds you will see the Oracle Database 12c splash screen.

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4. Step 1 : Configure Security Updates : Un-tick the tick-box and click the Next button. A warning message will appear. You can click on the Yes button to proceed.

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5. Step 2 : Installation Options : select the Create and Configure a Database option and then click the Next button.

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6. Step 3 : System Class : Select the Server Class option and then click the Next button.

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7. Step 4 : Grid Installation Options : Select the Single Instance Database Installation option and then click the next button.

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8. Step 5 : Select Install Type : Select the Typical install option and then click the Next button.

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9. Step 6 : Oracle Home User Selection : Select the Use Windows Built-in Account option and then click the Next button. A warning message appears. Click the Yes button.

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10. Step 7 : Typical Install Configuration : Set Global Database Name to cdb12c for the container database name. Set the Administrative password for the container database. Set the name of the pluggable database that will be created. Set this to pdb12c. Or you can accept the default names. Then click the Next button. If you get a warning message saying the password does not conform to the recommended standards, you can click the Yes button to ignore this warning and proceed.

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11. Step 8 : Prerequisite Checks : the install will check to see that you have enough space and necessary permissions etc.

12. Step 9 : Summary : When the prerequisite checks (like checking you have enough space and privileges) are finished you will get a window like the following.

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13. Step 10 : Install : You are now ready to start the install process. To do this click on the Install button in the Summary screen.

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You can now sit back, relax and watch the installation of 12.1.0.2c (with the in-memory option) complete.

You may get some Windows Security Alert windows pop up. Just click on the Allow Access button.

Then the Database Configuration Assistant will start. This step might take a while to complete.

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When everything is done you will get something like the following.

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Congratulations you now have Oracle Database 12.1.0.2c installed.

But you are not finished yet!!!

14. Add entry to TNSNAMES.ORA : you will need to add an entry to your tnsnames.ora file for the pluggable database. There is be an entry for the container DB but not for the pluggable. Here is what I added to my tnsnames.ora.

DB Install 14

The last step you need to do is to tell the container database to start up the pluggables when you reboot the server/laptop/PC/VM. To do this you will need to create the following trigger in the container DB.

sqlplus / as sysdba

CREATE or REPLACE trigger OPEN_ALL_PLUGGABLES

    after startup

    on database

BEGIN

    execute immediate ‘alter pluggable database all open’;

END open_all_pdbs;

Restart your database or machine and you plug gage DB ‘pdb12c’ will no automatically start.

You are all finished now 🙂

Enjoy 🙂

ORE now available for Multitenant (PDB) version of 12c

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Oracle has released an update to their Oracle R Enterprise software. We now have ORE 1.4.1 and this seems to have been released on the past day or so.

Here are the links to the important stuff:

ORE 1.4.1 Release Note

ORE 1.4.1 User Guide

ORE 1.4.1 Installation Guide

ORE 1.4.1 Download page

One of the main features of this new release is that it now supports the multi tenant option of the 12c database. Up to now if you wanted to use ORE and 12c then you needed to do a traditional install of the database. That means you would be just installing a single instance of the 12c database with no CDB or PDB.

With ORE 1.4.1 you can now install ORE into a PDB. It needs to be one of your current PDBs and should not be installed into the root PDB, otherwise it will not work. Check out the installation instructions using the links above.

As with all new releases there are a lot of bug fixes and perhaps some new ones too 🙂

Oracle R Enterprise and Oracle 12c

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A few of weeks ago we had the release of Oracle R Enterprise (ORE).

There has been some posts on the R/ORE on the Oracle discussion forums about installing ORE on Oracle 12c.

It turns out that the only way to install ORE on an Oracle 12c database is if you do a traditional install. What this means is that you do not have a CDB and PDBs configuration of Oracle 12c.

I’ll assume that Oracle are currently working on this particular issue, as you can imagine that that there is considerable amount of complexity in getting ORE to work with the PDBs.

If you are not using Oracle 12c then you are OK, as long as you are using 11.2.0.3 or 11.2.0.4 versions of the database. If you are using a lower version of the 11.2 database then you need to apply a patch to allow ORE to run.

As they say I’m sure it will be “fixed in the next release” 🙂

Schema Table Filtering for Oracle Data Miner

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If you have been using Oracle Data Miner, that is part of SQL Developer 4 or SQL Developer 3, you will notice that your schema can get filled up with various tables that are created by your workflows. The following image gives an example.

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These tables can include details of the various algorithms used and their settings, sample tables that were created using the various nodes, etc.  Basically they contain all the information that was setup by each node. Not every node in your workflow will create a table, but a lot do in particular if you have set the Cache or Sample in the Properties tab.

In most cases you do not need to be aware of or use most of these tables.

So How do I hide them, so that my schema table listing only shows me the main tables in my schema ?  By main tables, I mean the tables that you would expect to have in your schema before you started using Oracle Data Miner.

The answer to this question is to apply filters to your tables in SQL Developer. To do this go to your schema in the Connections tab. Expand to get the full list of schema objects and then right click on Tables. You should get a menu like the following.

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Select Apply Filter from the menu and the Apply Filter window will open. Here you can create filters to apply to the tables in your schema.

To restrict Oracle Data Miner related table you will need to exclude tables that begin with, DM$ and ODMR$. The following image shows these filters.

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When these filters are applied we only get our schema tables.

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There are two additional filters you may want to consider. The first of these is for the tables that begin with OUTPUT. These are tables that are created when you build a node sends the outputs from running a model to a table, or some other scenario where the output is sent to a table. In reality this is bad naming and we should use a name that is more meaningful, and reflects the contents of the table. But sometimes you just want to spool the outputs to a table and the name is not important. I have an additional filter to not show these tables (see below).

With SQL Developer 4, Oracle Data Miner seems to generate IOTs, as we can see in the above image. Again another filter can be created to exclude these from the list.

Here is the full list of filters.

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Depreciated ODM features in 12c

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With the release of the Oracle 12c Database there has been some changes to the Advanced Analytics options. Most of the new features both in the database and in the ODM tool have been documented in previous blog posts.
But what has been removed from the Advanced Analytics Option and what is not longer supported.
The first of these is the Java API that Oracle supplied many, many years ago. They have been saying for a few years now and since the release of 11.2g that these Java APIs are no longer supported. Again the documentation states this and the demo scripts are not included in the latest SQL Developer 4.  Instead of using the Java APIs you can using the in-database SQL functions and procedures.
One of the in-database DM algorithms was the Adaptive Bayes Network (ABN). Although this was de-supported in 11.2g of the database is was still in the database. This was to give customers who were still using it time to migrate to using the other algorithms. In 12c the ABN algorithm is not in the the database.  Before you upgrade your 11.2.x Oracle database to 12c you will need to drop any ABN models that you have in your database

12c New Data Mining functions

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With the release of Oracle 12c we get new functions/procedures and some updated ones for Oracle Data Miner that is part of the Advanced Analytics option.

The following are the new functions/procedures and the functions/procedures that have been updated in 12c, with a link to the 12c Documentation that explains what they do.

  • CLUSTER_DETAILS is a new function that predicts cluster membership for each row. It can use a pre-defined clustering model or perform dynamic clustering. The function returns an XML string that describes the predicted cluster or a specified cluster.

  • CLUSTER_DISTANCE is a new function that predicts cluster membership for each row. It can use a pre-defined clustering model or perform dynamic clustering. The function returns the raw distance between each row and the centroid of either the predicted cluster or a specified.

  • CLUSTER_ID has been enhanced so that it can either use a pre-defined clustering model or perform dynamic clustering.

  • CLUSTER_PROBABILITY has been enhanced so that it can either use a pre-defined clustering model or perform dynamic clustering. The data type of the return value has been changed from NUMBER to BINARY_DOUBLE.

  • CLUSTER_SET has been enhanced so that it can either use a pre-defined clustering model or perform dynamic clustering. The data type of the returned probability has been changed from NUMBER to BINARY_DOUBLE

  • FEATURE_DETAILS is a new function that predicts feature matches for each row. It can use a pre-defined feature extraction model or perform dynamic feature extraction. The function returns an XML string that describes the predicted feature or a specified feature.

  • FEATURE_ID has been enhanced so that it can either use a pre-defined feature extraction model or perform dynamic feature extraction.

  • FEATURE_SET has been enhanced so that it can either use a pre-defined feature extraction model or perform dynamic feature extraction. The data type of the returned probability has been changed from NUMBER to BINARY_DOUBLE.

  • FEATURE_VALUE has been enhanced so that it can either use a pre-defined feature extraction model or perform dynamic feature extraction. The data type of the return value has been changed from NUMBER to BINARY_DOUBLE.

  • PREDICTION has been enhanced so that it can either use a pre-defined predictive model or perform dynamic prediction.

  • PREDICTION_BOUNDS now returns the upper and lower bounds of the prediction as the BINARY_DOUBLE data type. It previously returned these values as the NUMBER data type.

  • PREDICTION_COST has been enhanced so that it can either use a pre-defined predictive model or perform dynamic prediction. The data type of the returned cost has been changed from NUMBER to BINARY_DOUBLE.

  • PREDICTION_DETAILS has been enhanced so that it can either use a pre-defined predictive model or perform dynamic prediction.

  • PREDICTION_PROBABILITY has been enhanced so that it can either use a pre-defined predictive model or perform dynamic prediction. The data type of the returned probability has been changed from NUMBER to BINARY_DOUBLE.

  • PREDICTION_SET has been enhanced so that it can either use a pre-defined predictive model or perform dynamic prediction. The data type of the returned probability has been changed from NUMBER to BINARY_DOUBLE.

Oracle Data Miner New Features (SQL Dev 4)

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With the release of the new Oracle 12c database and SQL Developer 4 we have a range of Oracle Data Miner new features . Some of these are embedded into the database and are only available in 12c. Check out my previous blog post on these new features.

In this blog post I will look at the new Oracle Data Miner features that come with the ODM tool in SQL Developer4.

The new features of the Oracle Data Miner tool can be grouped into 2 categories. The first category contains the new features that are available to all user of the tool (11.2g and 12c). The second category contains the new features that are only available in 12c. The new features of each of these categories will be explained below.

Category 1 – Common new features for 11.2g and 12c Database users

There is a new View Data feature that allows you to drill down to view the customer object and to view nested tables.

A new Graph Node that allows you to create graphs such as line, bar, scatter and boxplots for data at any stage of a workflow. You can specify any of the attributes from the data source for the graphs. You don’t seem to be limited to the number of graphs you can create.

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A new SQL Node. This is welcome addition, as there has been many times that I’ve need to write some SQL or PL/SQL to do a specific piece of processing on the data that was not available with the other nodes. There are 2 important elements to this SQL node really. The first is that you can write SQL and PL/SQL code to do whatever processing you want to do. But you can only do it on the Data node you are connected to.

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The second is that you can use it to call some ORE code. This allows you to use the power of R and extensive range of packages that are available to expand the analytic functionality that is available in the database. If there is some particular function that you cannot do in Oracle and it is available in R, you can now embed this function/code as an ORE object in the database. You can then called using SQL. 

WARNING: this particular feature will only work if you have ORE installed on your 11.2.0.3g or 12.1c database

New Model Build Node features, include node level text specifications for text transformations, displays the heuristic rules responsible for excluding predictor columns and being able to control the amount of classification and regression test results that are generated.  I’ll be covering these in later blog posts.

New Workflow SQL Script Deployment features. Up to now the workflow SQL script, I found to be of limited use. The development team have put a lot of work into generating a proper script that can be used by developers and DBA. But there are some limitations still. You can use the script will run the workflow automatically in the database without having the use the ODM tool. But it can only be run the in the schema that the workflow was generated. You will still have to do a lot of coding (although a lot less than you used to) to get your ODM models and workflows to run in another schema or database.

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This will output the script to a file buried deep somewhere inside you SQL  Developer directory.  Unfortunately in the EA1 release, the size of this location field is small and scrolling has not been enabled. So you cannot (currently) scroll to the end of the field to see the actual location.  You can edit this location to have a different shorter location.

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Maybe this will be fixed for the official release.

Category 2 – New features for 12c Database users.

Now for the new features that are only visible when you are running ODM / SQL Dev 4 against a 12c database. No configuration changes are needed. The ODM tool checks to see what version of the database you are logging into. It will then present the available features based on the version of the database.

New Predictive Query nodes allows you to build a node based on the new non-transient feature in 12c called Predictive Queries (PQs). In SQL Developer we get 3 addition types of Predictive Queries. These can be used for Anomaly Detection, Clustering and Feature Extraction

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It is important to remember that underlying model produced by these PQs to not exist in the database after the query has executed. The model is created, used on the data and then the model deleted.

The Clustering node has the new algorithm Expectation Maximization in addition to the existing algorithms of K-Means and O-Cluster.

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The Feature Extraction node has the new algorithm called Principal Component Analysis in addition to the existing Non-Negative Matrix Factorization algorithm.

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Text Transformations are now built into the model build nodes. These text transformations will be part of the Automatic Data Processing steps for the model build nodes. This is illustrated in the above images.

The Generalized Linear Model that is part of the Classification Node has a Feature Selection option in the Algorithm Settings. The default setting is Ridge Regression. Now there is an additional option of using Feature Selection.

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Prediction Result Explanations gives the scoring details used to to explain why the prediction was made.

 

Look out for blog post on each of these new features.

Oracle 12c Books

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Oracle 12c is only a few days old and there are books available on Amazon. The carousels below list some of the books available on Amazon.com and Amazon.co.uk

Amazon.com Widgets

Amazon.co.uk Widgets

Upgrading your ODM Repository for SQL Dev 4

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For those users of Oracle Data Miner (ODM) that is part of SQL Developer, now that Oracle have finally released SQL Developer 4, you might want to upgrade to this new release. There are a lot of new features. Some of these are available for 11.2g and 12.1c databases and some are only available for 12.1c users.

I will have another blog post soon on the new Oracle Data Miner (ODM) features that are available in SQL Developer 4.

The instructions given below are what I did to upgrade so that I could use the new ODM tool/SQL Developer 4.

Step 1 – Install SQL Developer 4 : I have another blog post on what this involves, so check it out and complete the steps before you continue with the result of the steps below.

Step 2 – Make ODM Visible : After SQL Developer 4 opens you should see all your migrated connections. To make ODM visible you need to click on the Tools menu, select Oracle Data Miner and then Make Visible. This will open a number of tabs on the left hand side of SQL Developer. These will include Data Miner (connections), Workflow Structure and Workflow Jobs.

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Step 3 – Open an ODM Connection : Take one your ODM connections and double click on it. SQL Developer 4 / ODM will check what versions of the ODM repository exists in your database. If this is your first time connecting from SQL Developer 4, you will be told that you will need to upgrade your repository

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Step 4 – Upgrade the ODM Repository : Select the Yes button on the Upgrade Repository window. You will then be asked for the SYS password. If you do not have access to this you can talk nicely to your DBA and ask them to enter the password for you.

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You may or may not get a warning message like the following. Just click OK to continue.

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Step 5 – Start the Repository Upgrade : When the Migrate Data Miner Repository window opens, just click the Start button. 

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This might be a good time to go off an make yourself a coffee. The upgrade process tool approx. 8 minutes on my laptop. If you were running this on a server located somewhere then the script will take a little bit longer to run!

The progress bar will let you know how things are progressing. It also gives some messages to let you known at what stage of the process it is at.

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Step 6 – All finished : When the Repository Migration has finished you will get a window with a message saying Task Successfully Complete. Click on the Close button to close this window.

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Step 7 – Open an Existing Workflow : Just to make sure that everything has worked with the install and ODM Repository migration, open one of your existing workflows. If it opens then everything should be OK.

When you open the workflow, the new Workflow Editor tab opens on the right hand side of SQL Developer. This seems to have replaced the Component Palette we had with the pervious version of the ODM tool. Expand the headings under the Workflow Editor to see the different nodes that are available. Most of these are the same but we have 2 new nodes under the Data section. These are Graph and SQL Query. I’ll have more on these in another post or posts.

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Auto-Starting your pluggables in 12c

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After installing 12c you get your container database and a pluggable. But the problem that most people have is that when they restart their server or in my case my VMs the container database gets started but the pluggable database does not automatically start. This means that you have to manually go in an start it. But this is a pain. Surely there is an easy way to get your pluggable databases to start. You would have though that Oracle would have some easy way of doing this.  If there is, I haven’t found it yet.

But I have come across how to automatically start your 12c pluggable databases, using a trigger.

CREATE or REPLACE trigger OPEN_ALL_PLUGGABLES
   after startup
   on  database
BEGIN
   execute immediate ‘alter pluggable database all open’;
END open_all_pdbs;

Let us test this out.  I’ve started my VirtualBox VM that has 12c installed on Windows 7. Here is the code that I ran to verify that the container has been started and the pluggable is in MOUNTED mode.

C:\Users\oracle>sqlplus / as sysdba

SQL*Plus: Release 12.1.0.1.0 Production on Wed Jul 17 15:27:35 2013

Copyright (c) 1982, 2013, Oracle.  All rights reserved.

Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 – 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing opt
ions

SQL> select name,DB_UNIQUE_NAME from v$database;

NAME      DB_UNIQUE_NAME
——— ——————————
ORCL      orcl

SQL> SELECT v.name, v.open_mode, NVL(v.restricted, ‘n/a’) “RESTRICTED”, d.status

  2  FROM v$pdbs v, dba_pdbs d
  3  WHERE v.guid = d.guid
  4  ORDER BY v.create_scn;

NAME                           OPEN_MODE  RES STATUS
—————————— ———- — ————-
PDB$SEED                       READ ONLY  NO  NORMAL
PDB12C                         MOUNTED    n/a NORMAL

SQL>

Next we will create the procedure (given above).

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To test the automatic starting of the pluggables, we need to shut down the container database, by issuing the shutdown command.

SQL> shutdown
Database closed.
Database dismounted.
ORACLE instance shut down.

SQL> select name,DB_UNIQUE_NAME from v$database;
select name,DB_UNIQUE_NAME from v$database
*
ERROR at line 1:
ORA-01034: ORACLE not available
Process ID: 0
Session ID: 0 Serial number: 0

This shows us that the container database is shutdown.

Now we can start the container and test to see if the pluggable database is started automatically by the trigger.

SQL> startup
ORACLE instance started.

Total System Global Area  855982080 bytes
Fixed Size                  2408408 bytes
Variable Size             562036776 bytes
Database Buffers          285212672 bytes
Redo Buffers                6324224 bytes
Database mounted.
Database opened.
SQL>

SQL> select name,DB_UNIQUE_NAME from v$database;

NAME      DB_UNIQUE_NAME
——— ——————————
ORCL      orcl

SQL> select status from v$instance;

STATUS
————
OPEN

SQL> SELECT v.name, v.open_mode, NVL(v.restricted, ‘n/a’) “RESTRICTED”, d.status

  2  FROM v$pdbs v, dba_pdbs d
  3  WHERE v.guid = d.guid
  4  ORDER BY v.create_scn;

NAME                           OPEN_MODE  RES STATUS
—————————— ———- — ————-
PDB$SEED                       READ ONLY  NO  NORMAL
PDB12C                         READ WRITE NO  NORMAL

SQL>

We can see that the pluggable was started.

Installing & Setting up SQL Developer 4

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The EA1 (early adopter) release of SQL Developer is now available. The main reason that I’m interested in this tools is that it has the upgraded Oracle Data Mining workflow tool. I’ve been using SQL Developer for a long, long time.  I was lucky enough to see a demo of it before it was ever released, back ……(well a long, long time ago) when Barry McGillin gave a demo of what they called Project Raptor, to a small group of (12) Oracle users in the Oracle East Point office, Dublin, Ireland. Barry was one of a couple of developers who were developing Project Raptor.
The EA1 release of SQL Developer 4 comes without the JDK install. For SQL Developer 4 you will need to install JDK 1.7.  There is a link from the SQL Developer 4 download page.
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After installing JDK 1.7 or maybe you have it installed already, you are ready to setup SQL Developer 4. The following instructions are for installing SQL Developer 4 on Windows.
After downloading it from the download page, all you have to do is to unzip the download. There is no install program. You are almost ready to start using SQL Developer.
There are 2 types of setup for SQL Developer. The first is where you have not used SQL Developer before. Point 1 below shows what is involved with this scenario.  Point 2 below shows what is involved if you have used previous releases of SQL Developer.
0.   Common steps to installing and setting up SQL Developer

  • Unzip the SQL Developer 4 download file to a location where you want the software to be located.
  • Go down the directories to where the sqldeveloper.exe is located.
  • Create a shortcut on your desktop for this file.
  • Double click on the shortcut on your desktop
  • Enter the location where JDK 1.7 was installed
    • C:\Program Files\Java\jdk1.7.0_25
  • SQL Developer will start

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1.   Scenario: Env. that has not used SQL Dev before

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  • Double click on the connection to open the SQL Worksheet
  • Finally enjoy 12c Smile

2. Scenario: Previous releases of SQL Developer exist

  • When asked about importing preferences from your previous SQL Developer installation, say Yes. This will take the connections from the most recent version of SQL Developer that you have installed. If you want to change this click on the button and select the version from the list
  • The install will progress updating everything and pull in your connects.
  • When finished SQL Developer 4 will open
  • But before you get going you should test that your connections work. An easy way of doing this is to use the pingall command. Open a SQL worksheet, connect to one of your schemas (this will test that your connection works), type pingall and press F5. This will test all of your connections and tell you which ones are currently working and which connections are not (you will see a –1ms).
  • You can now enjoy SQL Developer 4.

During the install of SQL Developer 4 I had an error. After inserting the directory for Java, the progress bar of the loading window got to about 1cm, displaying Registering Extensions above it, and then the loading window closed. SQL Dev 4 did not open.  After various attempts at investigating the problem, it looks like the directory created in AppData (Windows 7) was corrupted in some way. The solution to this problem is to rename or remove the directory.
\AppData\Roaming\SQL Developer\system4.0.0.12.27
When you have renamed or removed this directory, try starting SQL Dev 4 again. Everything should work now. Well it did for me.
Many thanks to Turloch in Oracle for his help.