Tuesday, November 30, 2010

How to record a song played by your PC

If you are looking for something like the Windows Sound Recorder but more professional AND freeware, you are in the right place.

The best easy-to-use but nevertheless quite professional software out there is Audacity.

It is cross-platform, that means that it's not OS-dependent: you can get a version of it for Windows, Mac OS X and GNU/Linux too.

Believe me, unless you have very unusual needs, you'll be ready to get started immediately:
press REC to record, STOP to end the task, SAVE the project or EXPORT him as MP3, WAV or Ogg Vorbis. End of story.

Once you get more confident with it, you can do a lot of stuff without having special skills:
  • record multiple tracks (automatically, it creates a new track everytime you press Stop and Rec again), that you'll be able to mix down in a single one or to manage individually, according to your needs;
  • apply tons of effects (fade in/fade out, filters, normalize, reverse,..);
  • set ID3 Tags (meta-informations about Author, Title, Year, Genre,..)
  • synchronize tracks, generate noise and so on...
As usual for the open-source products, you can find a good guide for free too ;)

NOTE: If your system is playing, but your Audacity is NOT recording, you should check your INPUT AUDIO SETTINGS, and verify that Recording Control and Stereo Mix are both enabled.

To open Input Audio Settings:
  • Open your "Master Volume" window by double-clicking the speaker icon in the System Tray area (or through the Control Panel, Sound and Audio Device Properties, Volume, Advanced tab);
  • Click on Options menu, select Properties, drop down the combobox and select your Input peripheral (every soundcard has integrated an input and an output device);
  • Click ok and adjust the settings until they're good (recording volume affects the quality of the registration, so raise or lower it to an appropriate value).

Wednesday, November 17, 2010

Export and Import data in Oracle (including BLOB and XMLTYPE fields)

To copy data from one database schema to another: that's the point.
You never needed it before ? You will, no doubt. And at that moment, you'll find very handy the wizard functionality of Toad (or similar softwares).
To use it, just right-click on the desired table in the left column, select "Copy data to another schema" from the context menĂ¹ and follow the wizard.
You will be asked to select a destination connection (aka database), a destination user (aka schema), then to select the options you want to set: commit frequency (default is every 500 rows), append or truncate (delete+insert) mode, "Where" conditions and so on. Then press "Execute" and wait for the script to end.
Note that you can move data from a user to another user on the same database, or between different users of different databases too.
Great, you moved some data from one table to one identical table on a different place.

But wait... what if you have some BLOB or XMLTYPE fields ? They are very complex, huge fields, containing tons of bytes and they are not managed by Toad or by any other wizard I know (except for some expensive 3rd party tools that you need to buy just to do this single operation).

This is the interesting part of the post: Oracle itself provides some tools to export and import ANY kind of data without any problems.

These tools are EXP and IMP and they are two command-line executables given to you by the Oracle (Client, Server, doesn't matter) installer, if you choose to install Oracle Tools too. You can find them in the BIN folder, under your Oracle folder.

Their behavior is well explained in the Oracle Wiki, but let's see how to use them in a few seconds ;)
Remember to write all that stuff in a single row, I'm putting it on different lines to keep the code clean.

EXP syntax for dummies

EXP username/password@dbInstance
query=\" put_here_your_optional_query_conditions \"

Example n.1: export the hypothetical tables EMPLOYEES, CUSTOMERS and DOCUMENTS from a user "MySociety", password "myPass", located in a database mapped as "my_database" on tnsnames.ora, without where conditions, in the folder "myexports" located on C: drive in the file system, with subfolders for dumps and logs.

EXP MySociety/myPass@my_database file=C:\myexports\dmp\allthebigtables.dmp log=C:\myexports\logs\allthebigtables.txt tables=EMPLOYEES, CUSTOMERS, DOCUMENTS

Example n.2: export the same tables EMPLOYEES and CUSTOMERS, specifying that the field AGE of both must be over 50.

EXP MySociety/myPass@my_database file=C:\myexports\dmp\overFifty.dmp log=C:\myexports\logs\overFifty.txt tables=EMPLOYEES, CUSTOMERS query=\" where age>50 \"

Example n.3: export the same tables EMPLOYEES and CUSTOMERS, specifying that the field AGE of EMPLOYEES must be over 50, and the field AGE of CUSTOMERS must be under 25. You will need to write two rows and execute them consecutively to do that.

EXP MySociety/myPass@my_database file=C:\myexports\dmp\empOverFifty.dmp log=C:\myexports\logs\empOverFifty.txt tables=EMPLOYEES query=\" where age>50 \"

EXP MySociety/myPass@my_database file=C:\myexports\dmp\customerUnderTwentfive.dmp log=C:\myexports\logs\customerUnderTwentfive.txt tables=CUSTOMERS query=\" where age<25 \"

This script is so powerfull that it will read and export all the data from all the tables targeted in one single dump file. Now let's see how to import that data in a different database and schema.

IMP Syntax for dummies

IMP username/password@dbInstance

Example: we want to import the previously saved "allthebigtables.dmp" file into a database called "external_database", in a schema with username "YourSociety" and passowrd "yourPass"

IMP YourSociety/yourPass@external_database file=C:\myexports\dmp\allthebigtables.dmp log=C:\myexports\logs\allthebigtables_import.txt tables=EMPLOYEES, CUSTOMERS, DOCUMENTS ignore=Y

This will import all the data previously exported into the new database, ignoring possible constraints problems.

Now you are ready to backup or move all your data between all your database instances and schemas.

As a further step, it's a very good idea to create batch files to achieve this, especially if you think that the operation you are performing now will be repeated in the future (like moving data between different environments, for example from Production to Test).

To do this, open a text editor, create a new text file, put all the stuff you've written into it, and save it with the ".bat" extension.
To avoid confusion, I recommend to use at least one file for exports and another one for imports ;)
P.S: Remember to use full path before IMP or EXP, to be able to launch the batch file from any place on your system, without touching environment variables like PATH and CLASSPATH.

Feel free to comment if you find this post useful :)

Special thanks to Giovanni Galasso for the support.

Tuesday, November 16, 2010

Oracle fundamentals

If you are approaching Oracle (one of the biggest and widely used databases on the market) for the first time, there are some little hints you should (or, better, you MUST) know to start working on it.

First of all, you have to install an Oracle Client on your machine, in order to access your database(s).
No problems here, just launch the installer and press Next until it's over.

The second step is to add your specific database parameters to the Oracle configuration file, called TNSNAMES.ORA, and located under the path YOUR_ORACLE_DIRECTORY\network\ADMIN.

NOTE: Every time you will need to access a different Oracle database for the first time, you will need to add the data into this file, so it's importat to remember its name and location, and its configuration rules.

The configuration is quite simple, and well described in the Oracle Wiki:

# COMMENTS DESCRIBING THE INSTANCE BELOW (comments starts with # symbol)
<addressname> =

          (Host = <hostname>)
          (Port = <port>))
   (SERVICE_NAME = <sid>)

where addressname is the name of your database instance (i.e. MY_DATABASE), hostname is the physical address (i.e. "" or "mydb.mydomain.com"), port is the port where database is listening (i.e. 1521), and sid is the System ID (i.e. MY_SID).

Note: When you will be asked to provide a Connection String to your database, that string will be composed in the form:

, for example mydb.mydomain.com:1521:MY_SID

You will need that string every time you'll want to connect to your database directly through a software that doesn't depends on your computer settings, for example a Java web application (that runs on a server, not on your pc). In that case, according to your specific Application Server peculiarity, connection string will be something like jdbc:oracle:thin:@mydb.mydomain.com:1521:MY_SID.

But everytime you will need to connect to your database from your computer, through an utility like SQL*Plus or Quest Software's TOAD, you will refer the database using only its addressname, keeping the things easy, no need to remember stuff like port, sid or hostname, and no need to reopen the tnsnames.ora every time... just remember your addressname (MY_DATABASE in the example above).

Now you are ready to connect to your database.
Open the SQL*Plus utility, installed together with the Oracle Client and located (in Windows and by default installation) under the Programs Menu -> Oracle Folder -> Application Development.

It will ask you to enter the USERNAME, the PASSWORD and the HOSSTRING (addressname): enter them and press OK.
Congratulations, you are now browsing your database.

SQL*Plus has an owner syntax, you can find the details here; however, the simplest way to query your database is:
  1. Write your SQL statement, pressing Enter everytime you need a new line to keep the code clean (don't worry, it won't run);
  2. Press Enter once again on the last, empty row: this will end the command;
  3. Write RUN to execute the SQL statement (just recorded) in the SQL*Plus buffer.

Note that SQL*Plus is an important, fast and powerfull tool, but you will use it mainly for debugging and forensic purposes.
It's very likely that you will be provided with a 3rd party softwares like TOAD or one of its freeware alternatives (take a look at Oracle's SQL Developer, SQLTools or TOra, the last available for linux too) in order to manage your database in a productive way.