Blob

The Blob implementation does not allow in-place modification (they are 'copies', as reported by the DatabaseMetaData.locatorsUpdateCopies() method). Because of this, you should use the corresponding PreparedStatement.setBlob() or ResultSet.updateBlob() (in the case of updatable result sets) methods to save changes back to the database.

Starting with Connector/J version 3.1.0, you can emulate Blobs with locators by adding the property 'emulateLocators=true' to your JDBC URL. You must then use a column alias with the value of the column set to the actual name of the Blob column in the SELECT that you write to retrieve the Blob. The SELECT must also reference only one table, the table must have a primary key, and the SELECT must cover all columns that make up the primary key. The driver will then delay loading the actual Blob data until you retrieve the Blob and call retrieval methods (getInputStream(), getBytes(), and so forth) on it.

CallableStatement

Starting with Connector/J 3.1.1, stored procedures are supported when connecting to MySQL version 5.0 or newer via the CallableStatement interface. Currently, the getParameterMetaData() method of CallableStatement is not supported.

Clob

The Clob implementation does not allow in-place modification (they are 'copies', as reported by the DatabaseMetaData.locatorsUpdateCopies() method). Because of this, you should use the PreparedStatement.setClob() method to save changes back to the database. The JDBC API does not have a ResultSet.updateClob() method.

Connection

Unlike older versions of MM.MySQL the isClosed() method does not “ping” the server to determine if it is alive. In accordance with the JDBC specification, it only returns true if 'closed()' has been called on the connection. If you need to determine if the connection is still valid, you should issue a simple query, such as "SELECT 1". The driver will throw an exception if the connection is no longer valid.

DatabaseMetaData

Foreign Key information (getImported/ExportedKeys() and getCrossReference()) is only available from 'InnoDB'-type tables. However, the driver uses 'SHOW CREATE TABLE' to retrieve this information, so when other storage engines support foreign keys, the driver will transparently support them as well.

Driver

PreparedStatement

PreparedStatements are implemented by the driver, as MySQL does not have a prepared statement feature. Because of this, the driver does not implement getParameterMetaData() or getMetaData() as it would require the driver to have a complete SQL parser in the client.

Starting with version 3.1.0 MySQL Connector/J, server-side prepared statements and 'binary-encoded' result sets are used when the server supports them.

Take care when using a server-side prepared statement with “large” parameters that are set via setBinaryStream(), setAsciiStream(), setUnicodeStream(), setBlob(), or setClob(). If you want to re-execute the statement with any “large” parameter changed to a non-“large” parameter, it is necessary to call clearParameters() and set all parameters again. The reason for this is as follows:

Consequently, if you want to change the “type” of a parameter to a non-“large” one, you must call clearParameters() and set all parameters of the prepared statement again before it can be re-executed.

ResultSet

By default, ResultSets are completely retrieved and stored in memory. In most cases this is the most efficient way to operate, and due to the design of the MySQL network protocol is easier to implement. If you are working with ResultSets that have a large number of rows or large values, and can not allocate heap space in your JVM for the memory required, you can tell the driver to 'stream' the results back one row at a time.

To enable this functionality, you need to create a Statement instance in the following manner:

stmt = conn.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY,
              java.sql.ResultSet.CONCUR_READ_ONLY);
stmt.setFetchSize(Integer.MIN_VALUE);

The combination of a forward-only, read-only result set, with a fetch size of Integer.MIN_VALUE serves as a signal to the driver to “stream” result sets row-by-row. After this any result sets created with the statement will be retrieved row-by-row.

There are some caveats with this approach. You will have to read all of the rows in the result set (or close it) before you can issue any other queries on the connection, or an exception will be thrown.

The earliest the locks these statements hold can be released (whether they be MyISAM table-level locks or row-level locks in some other storage engine such as InnoDB) is when the statement completes.

If the statement is within scope of a transaction, then locks are released when the transaction completes (which implies that the statement needs to complete first). As with most other databases, statements are not complete until all the results pending on the statement are read or the active result set for the statement is closed.

Therefore, if using “streaming” results, you should process them as quickly as possible if you want to maintain concurrent access to the tables referenced by the statement producing the result set.

ResultSetMetaData

The "isAutoIncrement()" method only works when using MySQL servers 4.0 and newer.

Statement

When using versions of the JDBC driver earlier than 3.2.1, and connected to server versions earlier than 5.0.3, the "setFetchSize()" method has no effect, other than to toggle result set streaming as described above.

MySQL does not support SQL cursors, and the JDBC driver doesn't emulate them, so "setCursorName()" has no effect.