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Use the
SQLConnection.attach()
method
to open a connection to an additional database on a
SQLConnection
instance
that already has an open database. You give the attached database
a name using the name parameter in the
attach()
method
call. When writing statements to manipulate that database, you can
then use that name in a prefix (using the form
database-name.table-name
)
to qualify any table names in your SQL statements, indicating to
the runtime that the table can be found in the named database.
You can execute a single SQL statement that includes tables from
multiple databases that are connected to the same SQLConnection
instance. If a transaction is created on the SQLConnection instance,
that transaction applies to all SQL statements that are executed
using the SQLConnection instance. This is true regardless of which
attached database the statement runs on.
Alternatively, you can also create multiple SQLConnection instances
in an application, each of which is connected to one or multiple
databases. However, if you do use multiple connections to the same
database keep in mind that a database transaction isn’t shared across
SQLConnection instances. Consequently, if you connect to the same
database file using multiple SQLConnection instances, you can’t
rely on both connections’ data changes being applied in the expected manner.
For example, if two
UPDATE
or
DELETE
statements
are run against the same database through different SQLConnection
instances, and an application error occurs after one operation takes
place, the database data could be left in an intermediate state
that would not be reversible and might affect the integrity of the
database (and consequently the application).
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