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/*!

    \page sql-driver.html

    \title SQL Database Drivers

    \brief How to configure and install QtSql drivers for supported databases.

    \ingroup best-practices

    The QtSql module uses driver \l{How to Create Qt

    Plugins}{plugins} to communicate with the different database

    APIs. Since Qt's SQL Module API is database-independent, all

    database-specific code is contained within these drivers. Several

    drivers are supplied with Qt and other drivers can be added. The

    driver source code is supplied and can be used as a model for

    \l{#development}{writing your own drivers}.

    \tableofcontents

    \section1 Supported Databases

    The table below lists the drivers included with Qt. Due to

    license incompatibilities with the GPL, not all of the plugins

    are provided with Open Source Versions of Qt.

    \table

    \header \o Driver name \o DBMS

    \row \o \link #QDB2 QDB2\endlink \o IBM DB2 (version 7.1 and above)

    \row \o \link #QIBASE QIBASE\endlink \o Borland InterBase

    \row \o \link #QMYSQL QMYSQL\endlink \o MySQL

    \row \o \link #QOCI QOCI\endlink \o Oracle Call Interface Driver

    \row \o \link #QODBC QODBC\endlink

         \o Open Database Connectivity (ODBC) - Microsoft SQL Server and other

            ODBC-compliant databases

    \row \o \link #QPSQL QPSQL\endlink \o PostgreSQL (versions 7.3 and above)

    \row \o \link #QSQLITE2 QSQLITE2\endlink \o SQLite version 2

    \row \o \link #QSQLITE QSQLITE\endlink \o SQLite version 3

    \row \o \link #QTDS QTDS\endlink \o Sybase Adaptive Server

    \endtable

    SQLite is the in-process database system with the best test coverage

    and support on all platforms. Oracle via OCI, and PostreSQL and MySQL

    through either ODBC or a native driver are well-tested on Windows and

    Linux. The completeness of the support for other systems depends on the

    availability and quality of client libraries.

    \bold{Note:} To build a driver plugin you need to have the appropriate

    client library for your Database Management System (DBMS). This provides

    access to the API exposed by the DBMS, and is typically shipped with it.

    Most installation programs also allow you to install "development

    libraries", and these are what you need. These libraries are responsible

    for the low-level communication with the DBMS.

    \target building

    \section1 Building the Drivers Using Configure

    On Unix and Mac OS X, the Qt \c configure script tries to

    automatically detect the available client libraries on your

    machine. Run \c{configure -help} to see what drivers can be

    built. You should get an output similar to this:

    \snippet doc/src/snippets/code/doc_src_sql-driver.qdoc 0

    The \c configure script cannot detect the neccessary libraries

    and include files if they are not in the standard paths, so it

    may be necessary to specify these paths using the \c -I and \c -L

    command-line options. For example, if your MySQL include files

    are installed in \c /usr/local/mysql (or in \c{C:\mysql\include}

    on Windows), then pass the following parameter to configure: \c

    -I/usr/local/mysql (or \c{-I C:\mysql\include} for Windows).

    On Windows the \c -I parameter doesn't accept spaces in

    filenames, so use the 8.3 name instead; for example, use

    \c{C:\progra~1\mysql} instead of \c{C:\Program Files\mysql}.

    Use the \c{-qt-sql-<driver>} parameter to build the database driver

    statically into your Qt library or \c{-plugin-sql-<driver>} to build

    the driver as a plugin. Look at the sections that follow for

    additional information about required libraries.

    \target buildingmanually

    \section1 Building the Plugins Manually

    \target QMYSQL

    \section2 QMYSQL for MySQL 4 and higher

    \section3 QMYSQL Stored Procedure Support

    MySQL 5 introduces stored procedure support at the SQL level, but no

    API to control IN, OUT and INOUT parameters. Therefore, parameters

    have to be set and read using SQL commands instead of QSqlQuery::bindValue().

    Example stored procedure:

    \snippet doc/src/snippets/code/doc_src_sql-driver.qdoc 1

    Source code to access the OUT values:

    \snippet doc/src/snippets/code/doc_src_sql-driver.qdoc 2

    \bold{Note:} \c{@outval1} and \c{@outval2} are variables local to the current

    connection and will not be affected by queries sent from another host

    or connection.

    \section3 Embedded MySQL Server

    The MySQL embedded server is a drop-in replacement for the normal

    client library. With the embedded MySQL server, a MySQL server is

    not required to use MySQL functionality.

    To use the embedded MySQL server, simply link the Qt plugin to \c

    libmysqld instead of libmysqlclient. This can be done by replacing

    \c -lmysqlclient_r by \c -lmysqld in the \c qmake command in the

    section below.

    Please refer to the MySQL documentation, chapter "libmysqld, the Embedded

    MySQL Server Library" for more information about the MySQL embedded server.

    \section3 How to Build the QMYSQL Plugin on Unix and Mac OS X

    You need the MySQL header files and as well as the shared library

    \c{libmysqlclient.so}. Depending on your Linux distribution you may

    need to install a package which is usually called "mysql-devel".

    Tell \l qmake where to find the MySQL header files and shared

    libraries (here it is assumed that MySQL is installed in

    \c{/usr/local}) and run \c{make}:

    \snippet doc/src/snippets/code/doc_src_sql-driver.qdoc 3

    After installing Qt, as described in the \l{Installing Qt on X11

    Platforms} document, you also need to install the plugin in the

    standard location:

    \snippet doc/src/snippets/code/doc_src_sql-driver.qdoc 4

    \section3 How to Build the QMYSQL Plugin on Windows

    You need to get the MySQL installation files. Run \c SETUP.EXE and

    choose "Custom Install". Install the "Libs & Include Files" Module.

    Build the plugin as follows (here it is assumed that MySQL is

    installed in \c{C:\MySQL}):

    \snippet doc/src/snippets/code/doc_src_sql-driver.qdoc 5

    If you are not using a Microsoft compiler, replace \c nmake with \c

    make in the line above.

    \note This database plugin is not supported for Windows CE.

    \note Including \c{"-o Makefile"} as an argument to \l qmake to

    tell it where to build the makefile can cause the plugin to be

    built in release mode only. If you are expecting a debug version

    to be built as well, don't use the \c{"-o Makefile"} option.

    \target QOCI

    \section2 QOCI for the Oracle Call Interface (OCI)

    \section3 General Information about the OCI plugin

    The Qt OCI plugin supports Oracle 9i, 10g and higher. After

    connecting to the Oracle server, the plugin will auto-detect the

    database version and enable features accordingly.

    It's possible to connect to a Oracle database without a tnsnames.ora file.

    This requires that the database SID is passed to the driver as the database

    name and that a hostname is given.

    \section3 OCI User Authentication

    The Qt OCI plugin supports authentication using

    external credentials (OCI_CRED_EXT). Usually, this means that the database

    server will use the user authentication provided by the operating system

    instead of its own authentication mechanism.

    Leave the username and password empty when opening a connection with

    QSqlDatabase to use the external credentials authentication.

    \section3 OCI BLOB/LOB Support

    Binary Large Objects (BLOBs) can be read and written, but be aware

    that this process may require a lot of memory. You should use a forward

    only query to select LOB fields (see QSqlQuery::setForwardOnly()).

    Inserting BLOBs should be done using either a prepared query where the

    BLOBs are bound to placeholders or QSqlTableModel, which uses a prepared

    query to do this internally.

    \section3 How to Build the OCI Plugin on Unix and Mac OS X

    For Oracle 10g, all you need is the "Instant Client Package - Basic" and

    "Instant Client Package - SDK". For Oracle prior to 10g, you require

    the standard Oracle client and the SDK packages.

    Oracle library files required to build the driver:

    \list

    \i \c libclntsh.so (all versions)

    \i \c libwtc9.so (only Oracle 9)

    \endlist

    Tell \c qmake where to find the Oracle header files and shared

    libraries and run make:

    For Oracle version 9:

    \snippet doc/src/snippets/code/doc_src_sql-driver.qdoc 6

    For Oracle version 10, we assume that you installed the RPM packages of the

    Instant Client Package SDK (you need to adjust the version number accordingly):

    \snippet doc/src/snippets/code/doc_src_sql-driver.qdoc 7

    \bold{Note:} If you are using the Oracle Instant Client package,

    you will need to set LD_LIBRARY_PATH when building the OCI SQL plugin

    and when running an applicaiton that uses the OCI SQL plugin. You can

    avoid this requirement by setting and RPATH and listing all of the

    libraries to link to. Here is an example:

    \snippet doc/src/snippets/code/doc_src_sql-driver.qdoc 32

    If you wish to build the OCI plugin manually with this method the procedure looks like this:

    \snippet doc/src/snippets/code/doc_src_sql-driver.qdoc 33

    \section3 How to Build the OCI Plugin on Windows

    Choosing the option "Programmer" in the Oracle Client Installer from

    the Oracle Client Installation CD is sufficient to build the plugin.

    Build the plugin as follows (here it is assumed that Oracle Client is

    installed in \c{C:\oracle}):

    \snippet doc/src/snippets/code/doc_src_sql-driver.qdoc 8

    If you are not using a Microsoft compiler, replace \c nmake with \c

    make in the line above.

    When you run your application you will also need to add the \c oci.dll

    path to your \c PATH environment variable:

    \snippet doc/src/snippets/code/doc_src_sql-driver.qdoc 9

    \bold{Note:} This database plugin is not supported for Windows CE.

    \target QODBC

    \section2 QODBC for Open Database Connectivity (ODBC)

    \section3 General Information about the ODBC plugin

    ODBC is a general interface that allows you to connect to multiple

    DBMSs using a common interface. The QODBC driver allows you to connect

    to an ODBC driver manager and access the available data sources. Note

    that you also need to install and configure ODBC drivers for the ODBC

    driver manager that is installed on your system. The QODBC plugin

    then allows you to use these data sources in your Qt applications.

    \bold{Note:} You should use native drivers in preference to the ODBC

    driver where they are available. ODBC support can be used as a fallback

    for compliant databases if no native drivers are available.

    On Windows an ODBC driver manager should be installed by default.

    For Unix systems there are some implementations which must be

    installed first. Note that every client that uses your application is

    required to have an ODBC driver manager installed, otherwise the

    QODBC plugin will not work.

    Be aware that when connecting to an ODBC datasource you must pass in

    the name of the ODBC datasource to the QSqlDatabase::setDatabaseName()

    function rather than the actual database name.

    The QODBC Plugin needs an ODBC compliant driver manager version 2.0 or

    later to work. Some ODBC drivers claim to be version 2.0 compliant,

    but do not offer all the necessary functionality. The QODBC plugin

    therefore checks whether the data source can be used after a

    connection has been established and refuses to work if the check

    fails. If you don't like this behavior, you can remove the \c{#define

    ODBC_CHECK_DRIVER} line from the file \c{qsql_odbc.cpp}. Do this at

    your own risk!

    By default, Qt instructs the ODBC driver to behave as an ODBC 2.x

    driver. However, for some \e{driver-manager/ODBC 3.x-driver}

    combinations (e.g., \e{unixODBC/MaxDB ODBC}), telling the ODBC

    driver to behave as a 2.x driver can cause the driver plugin to

    have unexpected behavior. To avoid this problem, instruct the ODBC

    driver to behave as a 3.x driver by

    \l{QSqlDatabase::setConnectOptions()} {setting the connect option}

    \c{"SQL_ATTR_ODBC_VERSION=SQL_OV_ODBC3"} before you

    \l{QSqlDatabase::open()} {open your database connection}. Note

    that this will affect multiple aspects of ODBC driver behavior,

    e.g., the SQLSTATEs.  Before setting this connect option, consult

    your ODBC documentation about behavior differences you can expect.

    If you experience very slow access of the ODBC datasource, make sure

    that ODBC call tracing is turned off in the ODBC datasource manager.

    Some drivers don't support scrollable cursors. In that case case only

    queries in forwardOnly mode can be used successfully.

    \section3 ODBC Stored Procedure Support

    With Microsoft SQL Server the result set returned by a stored

    procedure that uses the return statement, or returns multiple result

    sets, will be accessible only if you set the query's forward only

    mode to \e forward using \l QSqlQuery::setForwardOnly().

    \snippet doc/src/snippets/code/doc_src_sql-driver.qdoc 10

    \bold{Note:} The value returned by the stored procedure's return statement

    is discarded.

    \section3 ODBC Unicode Support

    The QODBC Plugin will use the Unicode API if UNICODE is defined. On

    Windows NT based systems, this is the default. Note that the ODBC

    driver and the DBMS must also support Unicode.

    Some driver managers and drivers don't support UNICODE. To use the

    QODBC plugin with such drivers it has to be compiled with the

    Q_ODBC_VERSION_2 defined.

    For the Oracle 9 ODBC driver (Windows), it is neccessary to check

    "SQL_WCHAR support" in the ODBC driver manager otherwise Oracle

    will convert all Unicode strings to local 8-bit.

    \section3 How to Build the ODBC Plugin on Unix and Mac OS X

    It is recommended that you use unixODBC. You can find the latest

    version and ODBC drivers at \l http://www.unixodbc.org.

    You need the unixODBC header files and shared libraries.

    Tell \c qmake where to find the unixODBC header files and shared

    libraries (here it is assumed that unixODBC is installed in

    \c{/usr/local/unixODBC}) and run \c{make}:

    \snippet doc/src/snippets/code/doc_src_sql-driver.qdoc 11

    \section3 How to Build the ODBC Plugin on Windows

    The ODBC header and include files should already be installed in the

    right directories. You just have to build the plugin as follows:

    \snippet doc/src/snippets/code/doc_src_sql-driver.qdoc 12

    If you are not using a Microsoft compiler, replace \c nmake with \c

    make in the line above.

    \bold{Note:} This database plugin is not officially supported for Windows CE.

    \target QPSQL

    \section2 QPSQL for PostgreSQL (Version 7.3 and Above)

    \section3 General Information about the QPSQL driver

    The QPSQL driver supports version 7.3 and higher of the PostgreSQL server.

    We recommend that you use a client library from version 7.3.15, 7.4.13,

    8.0.8, 8.1.4 or more recent as these versions contain security fixes, and

    as the QPSQL driver might not build with older versions of the client

    library depending on your platform.

    For more information about PostgreSQL visit \l http://www.postgresql.org.

    \section3 QPSQL Unicode Support

    The QPSQL driver automatically detects whether the PostgreSQL

    database you are connecting to supports Unicode or not. Unicode is

    automatically used if the server supports it. Note that the driver

    only supports the UTF-8 encoding. If your database uses any other

    encoding, the server must be compiled with Unicode conversion

    support.

    Unicode support was introduced in PostgreSQL version 7.1 and it will

    only work if both the server and the client library have been compiled

    with multibyte support. More information about how to set up a

    multibyte enabled PostgreSQL server can be found in the PostgreSQL

    Administrator Guide, Chapter 5.

    \section3 QPSQL BLOB Support

    Binary Large Objects are supported through the \c BYTEA field type in

    PostgreSQL server versions >= 7.1.

    \section3 How to Build the QPSQL Plugin on Unix and Mac OS X

    You need the PostgreSQL client library and headers installed.

    To make \c qmake find the PostgreSQL header files and shared

    libraries, run \c qmake the following way (assuming that the

    PostgreSQL client is installed in \c{/usr}):

    \snippet doc/src/snippets/code/doc_src_sql-driver.qdoc 13

    After installing Qt, as described in the \l{Installing Qt on X11 Platforms} document,

    you also need to install the plugin in the standard location:

    \snippet doc/src/snippets/code/doc_src_sql-driver.qdoc 14

    \section3 How to Build the QPSQL Plugin on Windows

    Install the appropriate PostgreSQL developer libraries for your

    compiler. Assuming that PostgreSQL was installed in \c{C:\psql},

    build the plugin as follows:

    \snippet doc/src/snippets/code/doc_src_sql-driver.qdoc 15

    Users of MinGW may wish to consult the following online document:

    \l{Compiling PostgreSQL On Native Win32 FAQ}.

    \bold{Note:} This database plugin is not supported for Windows CE.

    \target QTDS

    \section2 QTDS for Sybase Adaptive Server

    \section3 General Information about QTDS

    It is not possible to set the port with QSqlDatabase::setPort() due to limitations in the

    Sybase client library. Refer to the Sybase documentation for information on how to set up

    a Sybase client configuration file to enable connections to databases on non-default ports.

    \section3 How to Build the QTDS Plugin on Unix and Mac OS X

    Under Unix, two libraries are available which support the TDS protocol:

    \list

    \i FreeTDS, a free implementation of the TDS protocol

      (\l{http://www.freetds.org}). Note that FreeTDS is not yet stable,

      so some functionality may not work as expected.

    \i Sybase Open Client, available from \l{http://www.sybase.com}.

      Note for Linux users: Get the Open Client RPM from

      \l{http://linux.sybase.com}.

    \endlist

    Regardless of which library you use, the shared object file

    \c{libsybdb.so} is needed. Set the \c SYBASE environment variable to

    point to the directory where you installed the client library and

    execute \c{qmake}:

    \snippet doc/src/snippets/code/doc_src_sql-driver.qdoc 16

    \section3 How to Build the QDTS Plugin on Windows

    You can either use the DB-Library supplied by Microsoft or the Sybase

    Open Client (\l{http://www.sybase.com}). You must include \c

    NTWDBLIB.LIB to build the plugin:

    \snippet doc/src/snippets/code/doc_src_sql-driver.qdoc 17

    By default the Microsoft library is used on Windows, if you want to

    force the use of the Sybase Open Client, you must define \c

    Q_USE_SYBASE in \c{%QTDIR%\src\sql\drivers\tds\qsql_tds.cpp}. If you

    are not using a Microsoft compiler, replace \c nmake with \c make in

    the line above.

    \bold{Note:} This database plugin is not supported for Windows CE.

    \target QDB2

    \section2 QDB2 for IBM DB2 (Version 7.1 and Above)

    \section3 General Information about QDB2

    The Qt DB2 plugin makes it possible to access IBM DB2 databases. It

    has been tested with IBM DB2 v7.1 and 7.2. You must install the IBM

    DB2 development client library, which contains the header and library

    files necessary for compiling the QDB2 plugin.

    The QDB2 driver supports prepared queries, reading/writing of Unicode

    strings and reading/writing of BLOBs.

    We suggest using a forward-only query when calling stored procedures

    in DB2 (see QSqlQuery::setForwardOnly()).

    \section3 How to Build the QDB2 Plugin on Unix and Mac OS X

    \snippet doc/src/snippets/code/doc_src_sql-driver.qdoc 18

    After installing Qt, as described in the \l{Installing Qt on X11 Platforms} document,

    you also need to install the plugin in the standard location:

    \snippet doc/src/snippets/code/doc_src_sql-driver.qdoc 19

    \section3 How to Build the QDB2 Plugin on Windows

    The DB2 header and include files should already be installed in the

    right directories. You just have to build the plugin as follows:

    \snippet doc/src/snippets/code/doc_src_sql-driver.qdoc 20

    If you are not using a Microsoft compiler, replace \c nmake

    with \c make in the line above.

    \bold{Note:} This database plugin is not supported for Windows CE.

    \target QSQLITE2

    \section2 QSQLITE2 for SQLite Version 2