MySQL AB tries to keep the upgrade process as easy as possible, however as is the case with any software, sometimes changes need to be made in new versions to support new features, improve existing functionality, or comply with new standards.
This section has information about what users who are upgrading from one version of Connector/J to another (or to a new version of the MySQL server, with respect to JDBC functionality) should be aware of.
Connector/J 3.1 is designed to be backward-compatible with Connector/J 3.0 as much as possible. Major changes are isolated to new functionality exposed in MySQL-4.1 and newer, which includes Unicode character sets, server-side prepared statements, SQLState codes returned in error messages by the server and various performance enhancements that can be enabled or disabled via configuration properties.
Unicode Character Sets
— See the next section, as well as
Capítulo 10, Soporte de conjuntos de caracteres, for information on this new
feature of MySQL. If you have something misconfigured, it
will usually show up as an error with a message similar to
Illegal mix of collations.
Server-side Prepared Statements — Connector/J 3.1 will automatically detect and use server-side prepared statements when they are available (MySQL server version 4.1.0 and newer).
Starting with version 3.1.7, the driver scans SQL you are
preparing via all variants of
determine if it is a supported type of statement to
prepare on the server side, and if it is not supported by
the server, it instead prepares it as a client-side
emulated prepared statement. You can disable this feature
your JDBC URL.
If your application encounters issues with server-side prepared statements, you can revert to the older client-side emulated prepared statement code that is still presently used for MySQL servers older than 4.1.0 with the connection property useServerPrepStmts=false
Datetimes with all-zero
0000-00-00 ...) —
These values can not be represented reliably in Java.
Connector/J 3.0.x always converted them to NULL when being
read from a ResultSet.
Connector/J 3.1 throws an exception by default when these values are encountered as this is the most correct behavior according to the JDBC and SQL standards. This behavior can be modified using the zeroDateTimeBehavior configuration property. The allowable values are:
exception (the default), which
throws an SQLException with an SQLState of
convertToNull, which returns
NULL instead of the date.
round, which rounds the date to the
nearest closest value which is
Starting with Connector/J 3.1.7,
ResultSet.getString() can be decoupled
from this behavior via
default value is
false) so that you can
get retrieve the unaltered all-zero value as a String. It
should be noted that this also precludes using any time
zone conversions, therefore the driver will not allow you
to enable noDatetimeStringSync and
useTimezone at the same time.
New SQLState Codes — Connector/J 3.1 uses SQL:1999 SQLState codes returned by the MySQL server (if supported), which are different from the legacy X/Open state codes that Connector/J 3.0 uses. If connected to a MySQL server older than MySQL-4.1.0 (the oldest version to return SQLStates as part of the error code), the driver will use a built-in mapping. You can revert to the old mapping by using the configuration property useSqlStateCodes=false.
on a BLOB column will now return the address of the byte
array that represents it, instead of a String
representation of the BLOB. BLOBs have no character set,
so they can't be converted to java.lang.Strings without
data loss or corruption.
To store strings in MySQL with LOB behavior, use one of the TEXT types, which the driver will treat as a java.sql.Clob.
Debug builds —
Starting with Connector/J 3.1.8 a debug build of the
driver in a file named
is shipped alongside the normal binary jar file that is
Starting with Connector/J 3.1.9, we don't ship the .class files unbundled, they are only available in the JAR archives that ship with the driver.
You should not use the debug build of the driver unless
instructed to do so when reporting a problem or bug to
MySQL AB, as it is not designed to be run in production
environments, and will have adverse performance impact
when used. The debug binary also depends on the Aspect/J
runtime library, which is located in the
src/lib/aspectjrt.jar file that comes
with the Connector/J distribution.
Using the UTF-8 Character Encoding - Prior to MySQL server version 4.1, the UTF-8 character encoding was not supported by the server, however the JDBC driver could use it, allowing storage of multiple character sets in latin1 tables on the server.
Starting with MySQL-4.1, this functionality is deprecated. If you have applications that rely on this functionality, and can not upgrade them to use the official Unicode character support in MySQL server version 4.1 or newer, you should add the following property to your connection URL:
Server-side Prepared Statements - Connector/J 3.1 will automatically detect and use server-side prepared statements when they are available (MySQL server version 4.1.0 and newer). If your application encounters issues with server-side prepared statements, you can revert to the older client-side emulated prepared statement code that is still presently used for MySQL servers older than 4.1.0 with the following connection property:
Ésta es una traducción del manual de referencia de MySQL, que puede encontrarse en dev.mysql.com. El manual de referencia original de MySQL está escrito en inglés, y esta traducción no necesariamente está tan actualizada como la versión original. Para cualquier sugerencia sobre la traducción y para señalar errores de cualquier tipo, no dude en dirigirse a email@example.com.