Programming the Perl DBI

Statement Handles

Statement handles are the final type of object that DBI defines for database interaction and manipulation. These handles actually encapsulate individual SQL statements to be executed within the database.

Statement handles are children of their corresponding database handle. Since statement handles are objects in their own right, data within one statement is protected from tampering or modification by other statement handles.

For a given database handle, there is no practical limit to the number of statement handles that can be created and executed.^[33] Multiple statements can be created and executed within one script, and the data can be processed as it returns. A good example of this might be a data-mining robot that connects to a database, then executes a large number of queries that return all sorts of different types of information. Instead of attempting to write convoluted SQL to correlate the information within the database, the Perl script fetches all the data being returned from the many statements and performs analysis there, using the fully featured text and data manipulation routines that Perl has to offer.

Within the DBI specification and sample code, statement handles are generally referred to as $sth.

^[33] In reality, the number of concurrent statement handles is dependent on the underlying database. For information on how many concurrent statement handles your database can support, see Appendix B.