Programming the Perl DBI

General Interface Rules and Caveats

The DBI does not have a concept of a “current session.” Every session has a handle object (i.e., a $dbh) returned from the connect method. That handle object is used to invoke database-related methods.

Most data is returned to the Perl script as strings. (Null values are returned as undef.) This allows arbitrary precision numeric data to be handled without loss of accuracy. Beware that Perl may not preserve the same accuracy when the string is used as a number.

Dates and times are returned as character strings in the native format of the corresponding database engine. Time zone effects are database/driver-dependent.

Perl supports binary data in Perl strings, and the DBI will pass binary data to and from the driver without change. It is up to the driver implementors to decide how they wish to handle such binary data.

Most databases that understand multiple character sets have a default global charset. Text stored in the database is, or should be, stored in that charset; if not, then that’s the fault of either the database or the application that inserted the data. When text is fetched, it should be automatically converted to the charset of the client, presumably based on the locale. If a driver needs to set a flag to get that behavior, then it should do so; it should not require the application to do that.

Multiple SQL statements may not be combined in a single statement handle ($sth), although some databases and drivers do support this feature (notably ...