Before upgrading to MySQL 8.0, review the changes described in this section to identify those that apply to your current MySQL installation and applications. Perform any recommended actions.
Changes marked as Incompatible change are incompatibilities with earlier versions of MySQL, and may require your attention before upgrading. Our aim is to avoid these changes, but occasionally they are necessary to correct problems that would be worse than an incompatibility between releases. If an upgrade issue applicable to your installation involves an incompatibility, follow the instructions given in the description.
MySQL Server 8.0 incorporates a global data dictionary containing information about database objects in transactional tables. In previous MySQL series, dictionary data was stored in metadata files and nontransactional system tables. As a result, the upgrade procedure requires that you verify the upgrade readiness of your installation by checking specific prerequisites. For more information, see Section 10.5, “Preparing Your Installation for Upgrade”. A data dictionary-enabled server entails some general operational differences; see Data Dictionary Usage Differences.
sha256_password authentication plugins
provide more secure password encryption than the
mysql_native_password plugin, and
caching_sha2_password provides better
sha256_password. Due to
these superior security and performance characteristics of
caching_sha2_password, it is as of MySQL 8.0
the preferred authentication plugin, and is also the default
authentication plugin rather than
mysql_native_password. This change affects
both the server and the
For the server, the default value of the
default_authentication_pluginsystem variable changes from
This change applies only to new accounts created after installing or upgrading to MySQL 8.0 or higher. For accounts already existing in an upgraded installation, their authentication plugin remains unchanged. Existing users who wish to switch to
caching_sha2_passwordcan do so using the
ALTER USER user IDENTIFIED WITH caching_sha2_password BY 'password';
caching_sha2_passwordas the default authentication plugin rather than
The following sections discuss the implications of the more
prominent role of
If your MySQL installation must serve pre-8.0 clients and you
encounter compatibility issues after upgrading to MySQL 8.0 or
higher, the simplest way to address those issues and restore
pre-8.0 compatibility is to reconfigure the server to revert
to the previous default authentication plugin
mysql_native_password). For example, use
these lines in the server option file:
That setting enables pre-8.0 clients to connect to 8.0 servers
until such time as the clients and connectors in use at your
installation are upgraded to know about
caching_sha2_password. However, the setting
should be viewed as temporary, not as a long term or permanent
solution, because it causes new accounts created with the
setting in effect to forego the improved authentication
security provided by
The use of
caching_sha2_password offers more
secure password hashing than
mysql_native_password (and consequent
improved client connection authentication). However, it also has
compatibility implications that may affect existing MySQL
Clients and connectors that have not been updated to know about
caching_sha2_passwordmay have trouble connecting to a MySQL 8.0 server configured with
caching_sha2_passwordas the default authentication plugin, even to use accounts that do not authenticate with
caching_sha2_password. This issue occurs because the server specifies the name of its default authentication plugin to clients. If a client or connector is based on a client/server protocol implementation that does not gracefully handle an unrecognized default authentication plugin, it may fail with an error such as one of these:
Authentication plugin 'caching_sha2_password' is not supported
Authentication plugin 'caching_sha2_password' cannot be loaded: dlopen(/usr/local/mysql/lib/plugin/caching_sha2_password.so, 2): image not found
Warning: mysqli_connect(): The server requested authentication method unknown to the client [caching_sha2_password]
For information about writing connectors to gracefully handle requests from the server for unknown default authentication plugins, see Authentication Plugin Connector-Writing Considerations.
Clients that use an account that authenticates with
caching_sha2_passwordmust use either a secure connection (made using TCP using TLS/SSL credentials, a Unix socket file, or shared memory), or an unencrypted connection that supports password exchange using an RSA key pair. This security requirement does not apply to
mysql_native_passsword, so the switch to
caching_sha2_passwordmay require additional configuration (see Caching SHA-2 Pluggable Authentication). However, client connections in MySQL 8.0 prefer use of TLS/SSL by default, so clients that already conform to that preference may need no additional configuration.
Clients and connectors that have not been updated to know about
caching_sha2_passwordcannot connect to accounts that authenticate with
caching_sha2_passwordbecause they do not recognize this plugin as valid. (This is a particular instance of how client/server authentication plugin compatibility requirements apply, as discussed at Authentication Plugin Client/Server Compatibility.) To work around this issue, relink clients against
libmysqlclientfrom MySQL 8.0 or higher, or obtain an updated connector that recognizes
caching_sha2_passwordis also now the default authentication plugin in the
libmysqlclientclient library, authentication requires an extra round trip in the client/server protocol for connections from MySQL 8.0 clients to accounts that use
mysql_native_password(the previous default authentication plugin), unless the client program is invoked with a
libmysqlclient client library for pre-8.0
MySQL versions is able to connect to MySQL 8.0 servers (except
for accounts that authenticate with
caching_sha2_password). That means pre-8.0
clients based on
libmysqlclient should also
be able to connect. Examples:
Standard MySQL clients such as mysql and mysqladmin are
The DBD::mysql driver for Perl DBI is
MySQL Connector/Python has a C Extension module that is
libmysqlclient-based. To use it, include the
use_pure=Falseoption at connect time.
When an existing MySQL 8.0 installation is upgraded to MySQL
8.0.4 or higher, some older
libmysqlclient-based clients may
“automatically” upgrade if they are dynamically
linked, because they use the new client library installed by the
upgrade. For example, if the DBD::mysql driver for Perl DBI uses
dynamic linking, it can use the
libmysqlclient in place after an upgrade to
MySQL 8.0.4 or higher, with this result:
Prior to the upgrade, DBI scripts that use DBD::mysql can connect to a MySQL 8.0 server, except for accounts that authenticate with
After the upgrade, the same scripts become able to use
caching_sha2_passwordaccounts as well.
However, the preceding results occur because
libmysqlclient instances from MySQL 8.0
installations prior to 8.0.4 are binary compatible: They both
use a shared library major version number of 21. For clients
libmysqlclient from MySQL 5.7 or
older, they link to a shared library with a different version
number that is not binary compatible. In this case, the client
must be recompiled against
from 8.0.4 or higher for full compatibility with MySQL 8.0
MySQL Connector/J 5.1 through 8.0.8 is able to connect to MySQL 8.0 servers,
except for accounts that authenticate with
caching_sha2_password. (Connector/J 8.0.9 or higher
is required to connect to
Clients that use an implementation of the client/server protocol
libmysqlclient may need to be
upgraded to a newer version that understands the new
authentication plugin. For example, in PHP, MySQL connectivity
usually is based on
mysqlnd, which currently
does not know about
Until an updated version of
available, the way to enable PHP clients to connect to MySQL 8.0
is to reconfigure the server to revert to
mysql_native_password as the default
authentication plugin, as previously discussed.
If a client or connector supports an option to explicitly
specify a default authentication plugin, use it to name a plugin
Some MySQL clients support a
--default-authoption. (Standard MySQL clients such as mysql and mysqladmin support this option but can successfully connect to 8.0 servers without it. However, other clients may support a similar option. If so, it is worth trying it.)
Programs that use the
libmysqlclientC API can call the
mysql_options()function with the
MySQL Connector/Python scripts that use the native Python implementation of the client/server protocol can specify the
auth_pluginconnection option. (Alternatively, use the Connector/Python C Extension, which is able to connect to MySQL 8.0 servers without the need for
If a client or connector is available that has been updated to
caching_sha2_password, using it is
the best way to ensure compatibility when connecting to a MySQL
8.0 server configured with
caching_sha2_password as the default
These clients and connectors have been upgraded to support
libmysqlclientclient library in MySQL 8.0 (8.0.4 or higher). Standard MySQL clients such as mysql and mysqladmin are
libmysqlclient-based, so they are compatible as well.
libmysqlclientclient library in MySQL 5.7 (5.7.23 or higher). Standard MySQL clients such as mysql and mysqladmin are
libmysqlclient-based, so they are compatible as well.
MySQL Connector/C++ 1.1.11 or higher or 8.0.7 or higher.
MySQL Connector/J 8.0.9 or higher.
MySQL Connector/NET 8.0.10 or higher (through the classic MySQL protocol).
MySQL Connector/Node.js 8.0.9 or higher.
PHP: the X DevAPI PHP extension (mysql_xdevapi) supports
PHP: the PDO_MySQL and ext/mysqli extensions do not support
caching_sha2_password. In addition, when used with PHP versions before 7.1.16 and PHP 7.2 before 7.2.4, they fail to connect with
caching_sha2_passwordis not used.
For upgrades to MySQL 8.0, the authentication plugin existing
accounts remains unchanged, including the plugin for the
'root'@'localhost' administrative account.
For new MySQL 8.0 installations, when you initialize the data
directory (using the instructions at
Section 9.1, “Initializing the Data Directory”), the
'root'@'localhost' account is created, and
that account uses
default. To connect to the server following data directory
initialization, you must therefore use a client or connector
caching_sha2_password. If you
can do this but prefer that the
mysql_native_password after installation,
install MySQL and initialize the data directory as you normally
would. Then connect to the server as
ALTER USER as follows to
change the account authentication plugin and password:
ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY 'password';
If the client or connector that you use does not yet support
caching_sha2_password, you can use a modified
data directory-initialization procedure that associates the
root account with
mysql_native_password as soon as the account
is created. To do so, use either of these techniques:
--default-authentication-plugin=mysql_native_passwordoption along with
mysql_native_passwordin an option file, and name that option file using a
--defaults-fileoption along with
--initialize-insecure. (In this case, if you continue to use that option file for subsequent server startups, new accounts are created with
caching_sha2_passwordunless you remove the
default_authentication_pluginsetting from the option file.)
In replication scenarios for which all servers have been
upgraded to MySQL 8.0.4 or higher, replica connections to source
servers can use accounts that authenticate with
caching_sha2_password. For such connections,
the same requirement applies as for other clients that use
accounts that authenticate with
caching_sha2_password: Use a secure
connection or RSA-based password exchange.
To connect to a
for source/replica replication:
Use any of the following
CHANGE MASTER TOoptions:
MASTER_SSL = 1 GET_MASTER_PUBLIC_KEY = 1 MASTER_PUBLIC_KEY_PATH='path to RSA public key file'
Alternatively, you can use the RSA public key-related options if the required keys are supplied at server startup.
To connect to a
for Group Replication:
For MySQL built using OpenSSL, set any of the following system variables:
SET GLOBAL group_replication_recovery_use_ssl = ON; SET GLOBAL group_replication_recovery_get_public_key = 1; SET GLOBAL group_replication_recovery_public_key_path = 'path to RSA public key file';
Alternatively, you can use the RSA public key-related options if the required keys are supplied at server startup.
Incompatible change: A MySQL storage engine is now responsible for providing its own partitioning handler, and the MySQL server no longer provides generic partitioning support.
NDBare the only storage engines that provide a native partitioning handler that is supported in MySQL 8.0. A partitioned table using any other storage engine must be altered—either to convert it to
NDB, or to remove its partitioning—before upgrading the server, else it cannot be used afterwards.
For information about converting
InnoDB, see Converting Tables from MyISAM to InnoDB.
A table creation statement that would result in a partitioned table using a storage engine without such support fails with an error (ER_CHECK_NOT_IMPLEMENTED) in MySQL 8.0. If you import databases from a dump file created in MySQL 5.7 (or earlier) using mysqldump into a MySQL 8.0 server, you must make sure that any statements creating partitioned tables do not also specify an unsupported storage engine, either by removing any references to partitioning, or by specifying the storage engine as
InnoDBor allowing it to be set as
The procedure given at Section 10.5, “Preparing Your Installation for Upgrade”, describes how to identify partitioned tables that must be altered before upgrading to MySQL 8.0.
See Partitioning Limitations Relating to Storage Engines, for further information.
Incompatible change: Several server error codes are not used and have been removed (for a list, see Features Removed in MySQL 8.0). Applications that test specifically for any of them should be updated.
Important change: The default character set has changed from
utf8mb4. These system variables are affected:
As a result, the default character set and collation for new objects differ from previously unless an explicit character set and collation are specified. This includes databases and objects within them, such as tables, views, and stored programs. Assuming that the previous defaults were used, one way to preserve them is to start the server with these lines in the
[mysqld] character_set_server=latin1 collation_server=latin1_swedish_ci
In a replicated setting, when upgrading from MySQL 5.7 to 8.0, it is advisable to change the default character set back to the character set used in MySQL 5.7 before upgrading. After the upgrade is completed, the default character set can be changed to
Incompatible change: As of MySQL 8.0.11, it is prohibited to start the server with a
lower_case_table_namessetting that is different from the setting used when the server was initialized. The restriction is necessary because collations used by various data dictionary table fields are based on the
lower_case_table_namessetting that was defined when the server was initialized, and restarting the server with a different setting would introduce inconsistencies with respect to how identifiers are ordered and compared.
In MySQL 8.0.11, several deprecated features related to account management have been removed, such as use of the
GRANTstatement to modify nonprivilege characteristics of user accounts, the
NO_AUTO_CREATE_USERSQL mode, the
PASSWORD()function, and the
Replication from MySQL 5.7 to 8.0 of statements that refer to these removed features can cause replication failure. Applications that use any of the removed features should be revised to avoid them and use alternatives when possible, as described in Features Removed in MySQL 8.0.
To avoid a startup failure on MySQL 8.0, remove any instance of
sql_modesystem variable settings in MySQL option files.
Loading a dump file that includes the
NO_AUTO_CREATE_USERSQL mode in stored program definitions into a MySQL 8.0 server causes a failure. As of MySQL 5.7.24 and MySQL 8.0.13, mysqldump removes
NO_AUTO_CREATE_USERfrom stored program definitions. Dump files created with an earlier version of
mysqldumpmust be modified manually to remove instances of
In MySQL 8.0.11, these deprecated compatibility SQL modes were removed:
NO_TABLE_OPTIONS. They can no longer be assigned to the
sql_modesystem variable or used as permitted values for the mysqldump
Replication from MySQL 5.7 to 8.0 of statements that refer to the removed SQL modes can cause replication failure. This includes replication of
CREATEstatements for stored programs (stored procedures and functions, triggers, and events) that are executed while the current
sql_modevalue includes any of the removed modes. Applications that use any of the removed modes should be revised to avoid them.
As of MySQL 8.0.3, spatial data types permit an
SRIDattribute, to explicitly indicate the spatial reference system (SRS) for values stored in the column. See Spatial Data Types.
A spatial column with an explicit
SRIDattribute is SRID-restricted: The column takes only values with that ID, and
SPATIALindexes on the column become subject to use by the optimizer. The optimizer ignores
SPATIALindexes on spatial columns with no
SRIDattribute. See SPATIAL Index Optimization. If you want the optimizer to consider
SPATIALindexes on spatial columns that are not SRID-restricted, each such column should be modified:
Verify that all values within the column have the same SRID. To determine the SRIDs contained in a geometry column
col_name, use the following query:
SELECT DISTINCT ST_SRID(col_name) FROM tbl_name;
If the query returns more than one row, the column contains a mix of SRIDs. In that case, modify its contents so all values have the same SRID.
Redefine the column to have an explicit
Several spatial functions were removed in MySQL 8.0.0 due to a spatial function namespace change that implemented an
ST_prefix for functions that perform an exact operation, or an
MBRprefix for functions that perform an operation based on minimum bounding rectangles. The use of removed spatial functions in generated column definitions could cause an upgrade failure. Before upgrading, run mysqlcheck --check-upgrade for removed spatial functions and replace any that you find with their
MBRnamed replacements. For a list of removed spatial functions, refer to Features Removed in MySQL 8.0.
From MySQL 8.0.13, because of differences between row-based or mixed replication mode and statement-based replication mode in the way that temporary tables are handled, there are new restrictions on switching the binary logging format at runtime.
SET @@SESSION.binlog_formatcannot be used if the session has any open temporary tables.
SET @@persist.binlog_formatcannot be used if any replication channel has any open temporary tables.
SET @@persist_only.binlog_formatis allowed if replication channels have open temporary tables, because unlike
PERSIST_ONLYdoes not modify the runtime global system variable value.
SET @@persist.binlog_formatcannot be used if any replication channel applier is running. This is because the change only takes effect on a replication channel when its applier is restarted, at which time the replication channel might have open temporary tables. This behavior is more restrictive than before.
SET @@persist_only.binlog_formatis allowed if any replication channel applier is running.
Table 10.1 Renamed InnoDB Information Schema Views
Old Name New Name
After upgrading to MySQL 8.0.3 or higher, update any scripts that reference previous
The zlib library version bundled with MySQL was raised from version 1.2.3 to version 1.2.11.
compressBound()function in zlib 1.2.11 returns a slightly higher estimate of the buffer size required to compress a given length of bytes than it did in zlib version 1.2.3. The
compressBound()function is called by
InnoDBfunctions that determine the maximum row size permitted when creating compressed
InnoDBtables or inserting and updating rows in compressed
InnoDBtables. As a result,
CREATE TABLE ... ROW_FORMAT=COMPRESSED,
UPDATEoperations with row sizes very close to the maximum row size that were successful in earlier releases could now fail. To avoid this issue, test
CREATE TABLEstatements for compressed
InnoDBtables with large rows on a MySQL 8.0 test instance prior to upgrading.
With the introduction of the
--innodb-directoriesfeature, the location of file-per-table and general tablespace files created with an absolute path or in a location outside of the data directory should be added to the
innodb_directoriesargument value. Otherwise,
InnoDBis not able to locate these files during recovery. To view tablespace file locations, query the
SELECT TABLESPACE_NAME, FILE_NAME FROM INFORMATION_SCHEMA.FILES \G
Undo logs can no longer reside in the system tablespace. In MySQL 8.0, undo logs reside in two undo tablespaces by default. For more information, see Undo Tablespaces.
When upgrading from MySQL 5.7 to MySQL 8.0, any undo tablespaces that exist in the MySQL 5.7 instance are removed and replaced by two new default undo tablespaces. Default undo tablespaces are created in the location defined by the
innodb_undo_directoryvariable. If the
innodb_undo_directoryvariable is undefined, undo tablespaces are created in the data directory. Upgrade from MySQL 5.7 to MySQL 8.0 requires a slow shutdown which ensures that undo tablespaces in the MySQL 5.7 instance are empty, permitting them to be removed safely.
When upgrading to MySQL 8.0.14 or later from an earlier MySQL 8.0 release, undo tablespaces that exist in the pre-upgrade instance as a result of an
innodb_undo_tablespacessetting greater than 2 are treated as user-defined undo tablespaces, which can be deactivated and dropped using
ALTER UNDO TABLESPACEand
DROP UNDO TABLESPACEsyntax, respectively, after upgrading. Upgrade within the MySQL 8.0 release series may not always require a slow shutdown which means that existing undo tablespaces could contain undo logs. Therefore, existing undo tablespaces are not removed by the upgrade process.
Incompatible change: As of MySQL 8.0.17, the
CREATE TABLESPACE ... ADD DATAFILEclause does not permit circular directory references. For example, the circular directory reference (
/../) in the following statement is not permitted:
CREATE TABLESPACE ts1 ADD DATAFILE ts1.ibd 'any_directory/../ts1.ibd';
An exception to the restriction exists on Linux, where a circular directory reference is permitted if the preceding directory is a symbolic link. For example, the data file path in the example above is permitted if
any_directoryis a symbolic link. (It is still permitted for data file paths to begin with '
To avoid upgrade issues, remove any circular directory references from tablespace data file paths before upgrading to MySQL 8.0.17 or higher. To inspect tablespace paths, query the
Due to a regression introduced in MySQL 8.0.14, in-place upgrade on a case-sensitive file system from MySQL 5.7 or a MySQL 8.0 release prior to MySQL 8.0.14 to MySQL 8.0.16 failed for instances with partitioned tables and
lower_case_table_names=1. The failure was caused by a case mismatch issue related to partitioned table file names. The fix that introduced the regression was reverted, which permits upgrades to MySQL 8.0.17 from MySQL 5.7 or MySQL 8.0 releases prior to MySQL 8.0.14 to function as normal. However, the regression is still present in the MySQL 8.0.14, 8.0.15, and 8.0.16 releases.
In-place upgrade on a case-sensitive file system from MySQL 8.0.14, 8.0.15, or 8.0.16 to MySQL 8.0.17 fails with the following error when starting the server after upgrading binaries or packages to MySQL 8.0.17 if partitioned tables are present and
Upgrading from server version version_number with partitioned tables and lower_case_table_names == 1 on a case sensitive file system may cause issues, and is therefore prohibited. To upgrade anyway, restart the new server version with the command line option 'upgrade=FORCE'. When upgrade is completed, please execute 'RENAME TABLE part_table_name TO new_table_name; RENAME TABLE new_table_name TO part_table_name;' for each of the partitioned tables. Please see the documentation for further information.
If you encounter this error when upgrading to MySQL 8.0.17, perform the following workaround:
Restart the server with
--upgrade=forceto force the upgrade operation to proceed.
Identify partitioned table file names with lowercase partition name delimiters
mysql> SELECT FILE_NAME FROM INFORMATION_SCHEMA.FILES WHERE FILE_NAME LIKE '%#p#%' OR FILE_NAME LIKE '%#sp#%';
For each file identified, rename the associated table using a temporary name, then rename the table back to its original name.
mysql> RENAME TABLE table_name TO temporary_table_name; mysql> RENAME TABLE temporary_table_name TO table_name;
Verify that there are no partitioned table file names lowercase partition name delimiters (an empty result set should be returned).
mysql> SELECT FILE_NAME FROM INFORMATION_SCHEMA.FILES WHERE FILE_NAME LIKE '%#p#%' OR FILE_NAME LIKE '%#sp#%'; Empty set (0.00 sec)
ANALYZE TABLEon each renamed table to update the optimizer statistics in the
Because of the regression still present in the MySQL 8.0.14, 8.0.15, and 8.0.16 releases, importing partitioned tables from MySQL 8.0.14, 8.0.15, or 8.0.16 to MySQL 8.0.17 is not supported on case-sensitive file systems where
lower_case_table_names=1. Attempting to do so results in a “Tablespace is missing for table” error.
MySQL uses delimiter strings when constructing tablespace names and file names for table partitions. A “
#p#” delimiter string precedes partition names, and an “
#sp#” delimiter string precedes subpartition names, as shown:
Historically, delimiter strings have been uppercase (
#SP#) on case-sensitive file systems such as Linux, and lowercase (
#sp#) on case-insensitive file systems such as Windows. As of MySQL 8.0.19, delimiter strings are lowercase on all file systems. This change prevents issues when migrating data directories between case-sensitive and case-insensitive file systems. Uppercase delimiter strings are no longer used.
Additionally, partition tablespace names and file names generated based on user-specified partition or subpartition names, which can be specified in uppercase or lowercase, are now generated (and stored internally) in lowercase regardless of the
lower_case_table_namessetting to ensure case-insensitivity. For example, if a table partition is created with the name
PART_1, the tablespace name and file name are generated in lowercase:
During upgrade, MySQL checks and modifies if necessary:
Partition file names on disk and in the data dictionary to ensure lowercase delimiters and partition names.
Partition metadata in the data dictionary for related issues introduced by previous bug fixes.
InnoDBstatistics data for related issues introduced by previous bug fixes.
During tablespace import operations, partition tablespace file names on disk are checked and modified if necessary to ensure lowercase delimiters and partition names.
As of MySQL 8.0.21, a warning is written to the error log at startup or when upgrading from MySQL 5.7 if tablespace data files are found to reside in unknown directories. Known directories are those defined by the
innodb_directoriesvariables. To make a directory known, add it to the
innodb_directoriessetting. Making directories known ensures that data files can be found during recovery. For more information, see Tablespace Discovery During Crash Recovery.
Incompatible change: As of MySQL 8.0.13, the deprecated
GROUP BYclauses have been removed. Queries that previously relied on
GROUP BYsorting may produce results that differ from previous MySQL versions. To produce a given sort order, provide an
Queries and stored program definitions from MySQL 8.0.12 or lower that use
GROUP BYclauses should be amended. Otherwise, upgrading to MySQL 8.0.13 or higher may fail, as may replicating to MySQL 8.0.13 or higher replica servers.
Some keywords may be reserved in MySQL 8.0 that were not reserved in MySQL 5.7. See Keywords and Reserved Words. This can cause words previously used as identifiers to become illegal. To fix affected statements, use identifier quoting. See Schema Object Names.
After upgrading, it is recommended that you test optimizer hints specified in application code to ensure that the hints are still required to achieve the desired optimization strategy. Optimizer enhancements can sometimes render certain optimizer hints unnecessary. In some cases, an unnecessary optimizer hint may even be counterproductive.
Incompatible change: In MySQL 5.7, specifying a
FOREIGN KEYdefinition for an
InnoDBtable without a
CONSTRAINTclause, or specifying the
CONSTRAINTkeyword without a
InnoDBto use a generated constraint name. That behavior changed in MySQL 8.0, with
FOREIGN KEYvalue instead of a generated name. Because constraint names must be unique per schema (database), the change caused errors due to foreign key index names that were not unique per schema. To avoid such errors, the new constraint naming behavior has been reverted in MySQL 8.0.16, and
InnoDBonce again uses a generated constraint name.
For consistency with
NDBreleases based on MySQL 8.0.16 or higher use a generated constraint name if the
CONSTRAINTclause is not specified, or the
CONSTRAINTkeyword is specified without a
NDBreleases based on MySQL 5.7 and earlier MySQL 8.0 releases used the
The changes described above may introduce incompatibilities for applications that depend on the previous foreign key constraint naming behavior.