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 Data Definition (DDL) StatementsSHADOW 

Parameters for ALTER DATABASE

ADD (FILE)

Adds secondary files to the database.It is necessary to specify the full path to the file and the name of the secondary file.The description for the secondary file is similar to the one given for the CREATE DATABASE statement.

ADD DIFFERENCE FILE

Specifies the path and name of the difference file (or, delta file) that stores any mutations to the database whenever it is switched to the “copy-safe” mode.This clause does not add a file, but it configures name and path of the delta file when the database is in “copy-safe” mode.To change the existing setting, you should delete the previously specified description of the delta file using the DROP DIFFERENCE FILE clause before specifying the new description of the delta file.If the path and name of the delta file are not configured, the file will have the same path and name as the database, but with the .delta file extension.

Caution

If only a filename is specified, the delta file will be created in the current directory of the server.On Windows, this will be the system directory — a very unwise location to store volatile user files and contrary to Windows file system rules.
DROP DIFFERENCE FILE

Deletes the description (path and name) of the difference file specified previously in the ADD DIFFERENCE FILE clause.This does not delete a file, but DROP DIFFERENCE FILE clears (resets) the path and name of the delta file from the database header.Next time the database is switched to the “copy-safe” mode, the default values will be used (i.e. the same path and name as those of the database, but with the .delta extension).

BEGIN BACKUP

Switches the database to the “copy-safe” mode.ALTER DATABASE with this clause freezes the main database file, making it possible to back it up safely using file system tools, even if users are connected and performing operations with data.Until the backup state of the database is reverted to NORMAL, all changes made to the database will be written to the delta (difference) file.

Important

Despite its name, the ALTER DATABASE BEGIN BACKUP statement does not start a backup process, but only freezes the database, to create the conditions for doing a task that requires the database file to be read-only temporarily.
END BACKUP

Switches the database from the “copy-safe” mode to the normal mode.A statement with this clause merges the difference file with the main database file and restores the normal operation of the database.Once the END BACKUP process starts, the conditions no longer exist for creating safe backups by means of file system tools.

Warning

Use of BEGIN BACKUP and END BACKUP and copying the database files with filesystem tools, is not safe with multi-file databases!Use this method only on single-file databases.

Making a safe backup with the gbak utility remains possible at all times, although it is not recommended running gbak while the database is in LOCKED or MERGE state.
SET DEFAULT CHARACTER SET

Changes the default character set of the database.This change does not affect existing data or columns.The new default character set will only be used in subsequent DDL commands.To modify the default collation, use ALTER CHARACTER SET on the default character set of the database.

ENCRYPT WITH

See Encrypting a Database in the Security chapter.

DECRYPT

See Decrypting a Database in the Security chapter.

SET LINGER TO

Sets the linger-delay.The linger-delay applies only to Firebird SuperServer, and is the number of seconds the server keeps a database file (and its caches) open after the last connection to that database was closed.This can help to improve performance at low cost, when the database is opened and closed frequently, by keeping resources “warm” for the next connection.

Note

This mode can be useful for web applications — without a connection pool — where connections to the database usually “live” for a very short time.
Warning

The SET LINGER TO and DROP LINGER clauses can be combined in a single statement, but the last clause “wins”.For example, ALTER DATABASE SET LINGER TO 5 DROP LINGER will set the linger-delay to 0 (no linger), while ALTER DATABASE DROP LINGER SET LINGER to 5 will set the linger-delay to 5 seconds.
DROP LINGER

Drops the linger-delay (sets it to zero).Using DROP LINGER is equivalent to using SET LINGER TO 0.

Note

Dropping LINGER is not an ideal solution for the occasional need to turn it off for once-only operations where the server needs a forced shutdown.The gfix utility now has the -NoLinger switch, which will close the specified database immediately after the last attachment is gone, regardless of the LINGER setting in the database.The LINGER setting is retained and works normally the next time.

The same one-off override is also available through the Services API, using the tag isc_spb_prp_nolinger, e.g. (in one line):

fbsvcmgr host:service_mgr user sysdba password xxx
       action_properties dbname employee prp_nolinger
Warning

The DROP LINGER and SET LINGER TO clauses can be combined in a single statement, but the last clause “wins”.
SET DEFAULT SQL SECURITY

Specifies the default SQL SECURITY option to apply at runtime for objects without the SQL Security property set.See also SQL Security in chapter Security.

ENABLE PUBLICATION

Enables publication of this database for replication.Replication begins (or continues) with the next transaction started after this transaction commits.

DISABLE PUBLICATION

Enables publication of this database for replication.Replication is disabled immediately after commit.

EXCLUDE …​ FROM PUBLICATION

Excludes tables from publication.If the INCLUDE ALL TO PUBLICATION clause is used, all tables created afterward will also be replicated, unless overridden explicitly in the CREATE TABLE statement.

INCLUDE …​ TO PUBLICATION

Includes tables to publication.If the INCLUDE ALL TO PUBLICATION clause is used, all tables created afterward will also be replicated, unless overridden explicitly in the CREATE TABLE statement.

Note
Replication

  • Other than the syntax, configuring Firebird for replication is not covered in this language reference.

  • All replication management commands are DDL statements and thus effectively executed at the transaction commit time.

Examples of ALTER DATABASE Usage

  1. Adding a secondary file to the database.As soon as 30000 pages are filled in the previous primary or secondary file, the Firebird engine will start adding data to the secondary file test4.fdb.

    ALTER DATABASE
  ADD FILE 'D:\test4.fdb'
    STARTING AT PAGE 30001;

  2. Specifying the path and name of the delta file:

    ALTER DATABASE
  ADD DIFFERENCE FILE 'D:\test.diff';

  3. Deleting the description of the delta file:

    ALTER DATABASE
  DROP DIFFERENCE FILE;

  4. Switching the database to the “copy-safe” mode:

    ALTER DATABASE
  BEGIN BACKUP;

  5. Switching the database back from the “copy-safe” mode to the normal operation mode:

    ALTER DATABASE
  END BACKUP;

  6. Changing the default character set for a database to WIN1251

    ALTER DATABASE
  SET DEFAULT CHARACTER SET WIN1252;

  7. Setting a linger-delay of 30 seconds

    ALTER DATABASE
  SET LINGER TO 30;

  8. Encrypting the database with a plugin called DbCrypt

    ALTER DATABASE
  ENCRYPT WITH DbCrypt;

  9. Decrypting the database

    ALTER DATABASE
  DECRYPT;
See also

[fblangref50-ddl-db-create], [fblangref50-ddl-db-drop]