MySQL Backup and Recovery  /  ...  /  Dumping Data in SQL Format with mysqldump

1.4.1 Dumping Data in SQL Format with mysqldump

This section describes how to use mysqldump to create SQL-format dump files. For information about reloading such dump files, see Section 1.4.2, “Reloading SQL-Format Backups”.

By default, mysqldump writes information as SQL statements to the standard output. You can save the output in a file:

$> mysqldump [arguments] > file_name

To dump all databases, invoke mysqldump with the --all-databases option:

$> mysqldump --all-databases > dump.sql

To dump only specific databases, name them on the command line and use the --databases option:

$> mysqldump --databases db1 db2 db3 > dump.sql

The --databases option causes all names on the command line to be treated as database names. Without this option, mysqldump treats the first name as a database name and those following as table names.

With --all-databases or --databases, mysqldump writes CREATE DATABASE and USE statements prior to the dump output for each database. This ensures that when the dump file is reloaded, it creates each database if it does not exist and makes it the default database so database contents are loaded into the same database from which they came. If you want to cause the dump file to force a drop of each database before recreating it, use the --add-drop-database option as well. In this case, mysqldump writes a DROP DATABASE statement preceding each CREATE DATABASE statement.

To dump a single database, name it on the command line:

$> mysqldump --databases test > dump.sql

In the single-database case, it is permissible to omit the --databases option:

$> mysqldump test > dump.sql

The difference between the two preceding commands is that without --databases, the dump output contains no CREATE DATABASE or USE statements. This has several implications:

  • When you reload the dump file, you must specify a default database name so that the server knows which database to reload.

  • For reloading, you can specify a database name different from the original name, which enables you to reload the data into a different database.

  • If the database to be reloaded does not exist, you must create it first.

  • Because the output contains no CREATE DATABASE statement, the --add-drop-database option has no effect. If you use it, it produces no DROP DATABASE statement.

To dump only specific tables from a database, name them on the command line following the database name:

$> mysqldump test t1 t3 t7 > dump.sql

By default, if GTIDs are in use on the server where you create the dump file (gtid_mode=ON), mysqldump includes a SET @@GLOBAL.gtid_purged statement in the output to add the GTIDs from the gtid_executed set on the source server to the gtid_purged set on the target server. If you are dumping only specific databases or tables, it is important to note that the value that is included by mysqldump includes the GTIDs of all transactions in the gtid_executed set on the source server, even those that changed suppressed parts of the database, or other databases on the server that were not included in the partial dump. If you only replay one partial dump file on the target server, the extra GTIDs do not cause any problems with the future operation of that server. However, if you replay a second dump file on the target server that contains the same GTIDs (for example, another partial dump from the same source server), any SET @@GLOBAL.gtid_purged statement in the second dump file fails. To avoid this issue, either set the mysqldump option --set-gtid-purged to OFF or COMMENTED to output the second dump file without an active SET @@GLOBAL.gtid_purged statement, or remove the statement manually before replaying the dump file.