ABAP Keyword Documentation → ABAP - Reference → Processing External Data → ABAP - Database Accesses → Open SQL → Open SQL - Overview
Open SQL - Secondary Database Connections
You can use the CONNECTION addition to execute Open SQL commands on databases
other than the R/3 standard database. This gives you a number of possibilities, for example, you can transfer and update data in other databases. It is irrelevant whether the other database belongs to a
AS ABAP. However, it is
a prerequisite that it is a database system supported by SAP, because only in such a system is the software needed for an Open SQL access available in form of a shared library.
Other versions: 7.31 | 7.40 | 7.54
Setting Up a Secondary Database Connection
To a access another database you need an entry in the table DBCON that describes the access data of the database. If the secondary database is from a different manufacturer than the database of the current AS ABAP, you will need the SAP shared library as well as the client software provided by the manufacturer. Information on creating the DBCON entry and installing the additional software is described in the standard SAP Notes for every supported database system.
OnAS ABAP you can create and change entries in the DBCON database table using the central tool DBA Cockpit.
Standard Database Connection
Every work process has a standard database connection to the SAP standard database. It is communally
used by all internal sessions. You can also explicitly access this database connection using the name
DEFAULT. The DEFAULT connection can also be specified
dynamically using CONNECTION (name), where the name field must have the value 'DEFAULT'.
Accessing Other Database Tables
If you use a database connection to access database tables that are not in the SAP standard database,
there must also be a database table with the same name and identical type in the ABAP Dictionary of
the local AS ABAP. Open SQL assumes that the type information of these "remote" database tables corresponds
exactly with that of the local database table. This prerequisite is essential for the correct interpretation
of the database contents, for example, and, if necessary, their conversion with regards to the ABAP
type of the target fields (see INTO
Clause). If this prerequisite is not met, this can lead to wrong data or runtime errors when reading
or writing, depending on the database system. Because the ABAP runtime environment cannot ensure the
consistency of the type descriptions in the local and remote databases, the consistency must be guaranteed by the relevant application program.
Database Connections and Transactions
Every database connection forms its own transaction context. This means that database changes on one
connection can be saved (using COMMIT)
or discarded (using ROLLBACK)
independently of changes on other database connections. You can, for example, commit and store protocol data on a secondary database connection without affecting the current
transaction running on the standard SAP database connection.
Secondary database connections are not known outside the limits of an internal session. So, if a program opens a database connection and then calls another program - with SUBMIT for example - that opens a connection to the same database, you have two different connections and therefore two different database transactions.
For the first Open SQL commandthat requests a specific database connection, the system opens a corresponding connection. All subsequent commands (in the same internal session) for the same "remote" database use the same database connection and all form a database transaction. The transaction is ended by:
COMMIT CONNECTION or ROLLBACK CONNECTION on this connection
COMMIT WORK or ROLLBACK WORK
CALL DIALOG,
CALL TRANSACTION, MESSAGE
WAIT UNTIL.
In summary, a database transaction is completed at the latest, when the application program reaches a state in which a change of work process could occur.
Note
Working with parallel database connections, that is parallel transactions, can lead to lock situations that only one work process is involved in: A program changes a database row on the first connection and tries to change the same row on a second connection. This will result in the program waiting for the lock of the first transaction, without this first transaction ever being able to continue. You can only resolve this situation by ending the work process. This is done automatically for dialog processes, but must be done manually for background jobs. You should therefore not change the same table in one program on multiple database connections.
Interaction with Native SQL Connections.
In addition to the above, you can also explicitly open a connection using a CONNECT with
Native SQL. Native SQL also allows you to explicitly close
and disconnect a database connection using DISCONNECT. In this case, the
database transaction in question is closed and corresponding database changes are discarded. You can
use the Native SQL command GET CONNECTION to ascertain the current Native
SQL connection. With Native SQL you can also access a connection that was opened with Open SQL. In this
case it is sufficient to convert the active Native SQL connection using SET CONNECTION. It is not necessary to open it using CONNECT TO.
Management of Database Connections
The database connections are automatically managed by the runtime system. If a transaction is saved on a database connection
(COMMIT) or rolled back
(ROLLBACK), it can be reused
by the runtime system. You can open a maximum of 10 database connections for each work process. On certain databases, you may not be able to reach this number.