Tim Bunce , Alligator Descartes. DBI in the Real World.
A Historical Interlude and Standing Stones. Storage Managers and Layers. Query Languages and Data Functions. Standing Stones and the Sample Database. Error Handling. Utility Methods and Functions. Interacting with the Database. Binding Parameters to Statements. Binding Output Columns. Atomic and Batch Fetching. FlatFile Databases. Putting Complex Data into Flat Files. Concurrent Database Access and Locking.
Programming the Perl DBI - database programming with Perl
SQL and Relational Databases. So once our database connection is established, we are ready to make a query into this database. Following is the procedure to query all the records having AGE greater than This will take four steps. This will be done using prepare API. Fetching all the results one by one and printing those results.
Following is the procedure to update all the records having SEX as 'M'.
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Here we will increase AGE of all the males by one year. This will take three steps. See next section for commit and rollback APIs. There may be a case when condition is not given in advance.
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In some case you would like to set a value which is not given in advance so you can use binding value as follows. In this example income of all males will be set to This operation will take following steps. Executing SQL query to delete required records from the database. You can use do statement to execute any of the command as follows. Actually, if it succeeds it returns the number of affected rows.
In the example it would return the number of rows that were actually deleted. Commit is the operation which gives a green signal to database to finalize the changes and after this operation no change can be reverted to its orignal position.
Programming the Perl DBI: Database programming with Perl [FULL]
If you are not satisfied with all the changes or you encounter an error in between of any operation , you can revert those changes to use rollback API. Many databases support transactions. This means that you can make a whole bunch of queries which would modify the databases, but none of the changes are actually made. After the next commit or rollback, AutoCommit will automatically be turned on again.
If your transactions are simple, you can save yourself the trouble of having to issue a lot of commits.
When you make the connect call, you can specify an AutoCommit option which will perform an automatic commit operation after every successful query. Here's what it looks like:.
Programming the Perl DBI
When you make the connect call, you can specify a RaiseErrors option that handles errors for you automatically. When an error occurs, DBI will abort your program instead of returning a failure code. If all you want is to abort the program on an error, this can be convenient. The transaction behaviour of the disconnect method is, sadly, undefined.
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Some database systems such as Oracle and Ingres will automatically commit any outstanding changes, but others such as Informix will rollback any outstanding changes. Applications not using AutoCommit should explicitly call commit or rollback before calling disconnect. Undefined values, or undef, are used to indicate NULL values. These examples insert and update the column age with a NULL value:. At least for database engines that conform to the SQL standard. A simple technique is to prepare the appropriate statement as needed, and substitute the placeholder for non-NULL cases:. By default, a warning is given if some drivers are hidden by others of the same name in earlier directories.
Returns a list of driver name and driver handle pairs for all drivers 'installed' loaded into the current process. The driver name does not include the 'DBD::' prefix. Returns a list of data sources databases available via the named driver. Quote a string literal for use as a literal value in an SQL statement, by escaping any special characters such as quotation marks contained within the string and adding the required type of outer quotation marks.
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