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Encoding Data Matrix ECC200 in Visual Basic .NET Database Integrity Checks

The dba module, when used with the MySQL database, allows you to check the data integrity of your database. This is useful for routine maintenance as well as diagnosing problems. The Default Check Type field lets you tell MySQL which type of check to make. Here are the various

options on the admin/settings/dba page, as described by the MySQL documentation (http:// dev.mysql.com/doc/mysql/en/check-table.html): QUICK means don t scan the rows to check for incorrect links. FAST means to check only tables that haven t been closed properly. CHANGED means to check only tables that have been changed since the last check or haven t been closed properly. MEDIUM means to scan rows to verify that deleted links are okay. It also calculates a key checksum for the rows and verifies this with a calculated checksum for the keys. EXTENDED means to do a full key lookup for all keys for each row. This ensures that the table is 100% consistent, but takes a long time! In the unlikely event that the data integrity of your database becomes compromised, there is a chance that it can be automatically repaired. The Repair Option field lets you determine when the repair link for a table is visible. The best setting is Automatic, as this not only hides superfluous links, but also serves to alert you (by the presence of the link) when the data integrity has been broken.

To see an overview of the tables in your database, select administer database. For each table, you are shown the number of rows and have the following options: The View option shows the contents of the table. The Describe option shows the data structure of the table, as shown in Figure 4-19.

The Check option checks the table (and its indexes) for errors and integrity. The Repair option attempts to fix errors found with check. See the MySQL documentation (http://dev.mysql.com/doc/mysql/en/repair-table.html) for details. The Backup option saves one or more tables in the form of a SQL dump to a file that you specify. The Empty option deletes all data from the table. The Drop option removes the table from the database.

The dba module facilitates querying the database through SQL that you enter directly into the web browser or by using a file stored on your local machine. Using SQL that you type directly into the browser is a convenient way to run custom queries if you are familiar and comfortable with using SQL. To do this, select administer database and click the Query tab (admin/ database/query). You can also run scripts from files, which is an excellent tool for adding database definitions for modules that you are installing from files. To do this, select administer database and click the Script tab (admin/database/script).

The Devel module is an indispensable tool for programmers and system administrators who want to know how Drupal accesses the database. It collects all of the SQL queries that are made during the loading of a page and shows them as output at the bottom of the screen, along with the time they took and whether the same query was called more than once. This is an excellent way to start to understand what goes on behind the scenes in Drupal, as well as a means for spotting bottlenecks in performance. The Devel module also defines a couple of helper functions to be used for debugging while programming, integrates with Xdebug (http://www.xdebug.org/) to provide profiler information, and includes a number of scripts for generating dummy database data for the purposes of testing.

Download the latest version of the Devel module from http://drupal.org/project/devel. Create a modules/devel folder and move the devel.module file into it. Enable the module from the admin/modules page. The archive download comes with a devel/generated folder, which contains various scripts for automatically generating content in the database for the purpose of testing. Move these files to the server only if the site is a development site and you intend to use the scripts. Otherwise, you are best advised to omit them. If you are using Xdebug and wish to have access to profiler information through the Devel module, you should add information to either your php.ini file or the .htaccess file. For php.ini, add the following: