I had complied qsqlmysql.dll.

[jsulm]

@yuyu As @Christian-Ehrlicher suggested set QT_DEBUG_PLUGINS environment variable to 1 before running your app and then check its out put - it should tell you why qsqlmysql.dll could not be loaded.

[yuyu]

@jsulm I Had set but it tell me load error.I look up the qt doc.

I do not know what is mean the note.

[yuyu]

@jsulm said in I had complied qsqlmysql.dll.:

QT_DEBUG_PLUGINS

[jsulm]

@yuyu Please post text not images.
We need to see the actual error after :
Currently there are unreadable characters.

[yuyu]

@jsulm

qt.core.plugin.factoryloader: Got keys from plugin meta data QList("QSQLITE")
qt.core.plugin.factoryloader: looking at "C:/Qt/6.3.0/mingw_64/plugins/sqldrivers/qsqlmysql.dll"
qt.core.plugin.loader: Found metadata in lib C:/Qt/6.3.0/mingw_64/plugins/sqldrivers/qsqlmysql.dll, metadata=
{
    "IID": "org.qt-project.Qt.QSqlDriverFactoryInterface",
    "MetaData": {
        "Keys": [
            "QMYSQL",
            "QMARIADB"
        ]
    },
    "archlevel": 2,
    "className": "QMYSQLDriverPlugin",
    "debug": true,
    "version": 393984
}

qt.core.plugin.loader: QLibraryPrivate::loadPlugin failed on "C:/Qt/6.3.0/mingw_64/plugins/sqldrivers/qsqlmysql.dll" : "Cannot load library C:\\Qt\\6.3.0\\mingw_64\\plugins\\sqldrivers\\qsqlmysql.dll

I had success when i use mysql5.7 ,but the same way there has error when i use mysql8.0.22

[jsulm]

@yuyu said in I had complied qsqlmysql.dll.:

qsqlmysql.dll

In your other output there is some unreadable characters after qsqlmysql.dll:
Can you provide that part as readable text?

[yuyu]

@jsulm the unreadable characters is what I use qDebug output chineses，I had delete it.
now
mycode

 qDebug() << QSqlDatabase::drivers();

    QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
    db.setHostName("localhost");
    db.setPort(3306);
    db.setDatabaseName("mydb");
    db.setUserName("root");
    db.setPassword("123456");
    bool ok = db.open();

the console

16:45:13: Debugging D:\1a_perfect\build-testsql-Desktop_Qt_6_3_0_MinGW_64_bit-Debug\debug\testsql.exe ...
qt.core.plugin.factoryloader: checking directory path "C:/Qt/6.3.0/mingw_64/plugins/platforms" ...
qt.core.plugin.factoryloader: looking at "C:/Qt/6.3.0/mingw_64/plugins/platforms/qdirect2d.dll"
qt.core.plugin.loader: Found metadata in lib C:/Qt/6.3.0/mingw_64/plugins/platforms/qdirect2d.dll, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "direct2d"
        ]
    },
    "archlevel": 2,
    "className": "QWindowsDirect2DIntegrationPlugin",
    "debug": false,
    "version": 393984
}

qt.core.plugin.factoryloader: Got keys from plugin meta data QList("direct2d")
qt.core.plugin.factoryloader: looking at "C:/Qt/6.3.0/mingw_64/plugins/platforms/qminimal.dll"
qt.core.plugin.loader: Found metadata in lib C:/Qt/6.3.0/mingw_64/plugins/platforms/qminimal.dll, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "minimal"
        ]
    },
    "archlevel": 2,
    "className": "QMinimalIntegrationPlugin",
    "debug": false,
    "version": 393984
}

qt.core.plugin.factoryloader: Got keys from plugin meta data QList("minimal")
qt.core.plugin.factoryloader: looking at "C:/Qt/6.3.0/mingw_64/plugins/platforms/qoffscreen.dll"
qt.core.plugin.loader: Found metadata in lib C:/Qt/6.3.0/mingw_64/plugins/platforms/qoffscreen.dll, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "offscreen"
        ]
    },
    "archlevel": 2,
    "className": "QOffscreenIntegrationPlugin",
    "debug": false,
    "version": 393984
}

qt.core.plugin.factoryloader: Got keys from plugin meta data QList("offscreen")
qt.core.plugin.factoryloader: looking at "C:/Qt/6.3.0/mingw_64/plugins/platforms/qwindows.dll"
qt.core.plugin.loader: Found metadata in lib C:/Qt/6.3.0/mingw_64/plugins/platforms/qwindows.dll, metadata=
{
    "IID": "org.qt-project.Qt.QPA.QPlatformIntegrationFactoryInterface.5.3",
    "MetaData": {
        "Keys": [
            "windows"
        ]
    },
    "archlevel": 2,
    "className": "QWindowsIntegrationPlugin",
    "debug": false,
    "version": 393984
}

qt.core.plugin.factoryloader: Got keys from plugin meta data QList("windows")
qt.core.plugin.factoryloader: checking directory path "D:/1a_perfect/build-testsql-Desktop_Qt_6_3_0_MinGW_64_bit-Debug/debug/platforms" ...
qt.core.library: "C:/Qt/6.3.0/mingw_64/plugins/platforms/qwindows.dll" loaded library
qt.core.plugin.factoryloader: checking directory path "C:/Qt/6.3.0/mingw_64/plugins/platformthemes" ...
qt.core.plugin.factoryloader: checking directory path "D:/1a_perfect/build-testsql-Desktop_Qt_6_3_0_MinGW_64_bit-Debug/debug/platformthemes" ...
qt.core.plugin.factoryloader: checking directory path "C:/Qt/6.3.0/mingw_64/plugins/styles" ...
qt.core.plugin.factoryloader: looking at "C:/Qt/6.3.0/mingw_64/plugins/styles/qwindowsvistastyle.dll"
qt.core.plugin.loader: Found metadata in lib C:/Qt/6.3.0/mingw_64/plugins/styles/qwindowsvistastyle.dll, metadata=
{
    "IID": "org.qt-project.Qt.QStyleFactoryInterface",
    "MetaData": {
        "Keys": [
            "windowsvista"
        ]
    },
    "archlevel": 2,
    "className": "QWindowsVistaStylePlugin",
    "debug": false,
    "version": 393984
}

qt.core.plugin.factoryloader: Got keys from plugin meta data QList("windowsvista")
qt.core.plugin.factoryloader: checking directory path "D:/1a_perfect/build-testsql-Desktop_Qt_6_3_0_MinGW_64_bit-Debug/debug/styles" ...
qt.core.library: "C:/Qt/6.3.0/mingw_64/plugins/styles/qwindowsvistastyle.dll" loaded library
qt.core.plugin.factoryloader: checking directory path "C:/Qt/6.3.0/mingw_64/plugins/iconengines" ...
qt.core.plugin.factoryloader: looking at "C:/Qt/6.3.0/mingw_64/plugins/iconengines/qsvgicon.dll"
qt.core.plugin.loader: Found metadata in lib C:/Qt/6.3.0/mingw_64/plugins/iconengines/qsvgicon.dll, metadata=
{
    "IID": "org.qt-project.Qt.QIconEngineFactoryInterface",
    "MetaData": {
        "Keys": [
            "svg",
            "svgz",
            "svg.gz"
        ]
    },
    "archlevel": 2,
    "className": "QSvgIconPlugin",
    "debug": false,
    "version": 393984
}

qt.core.plugin.factoryloader: Got keys from plugin meta data QList("svg", "svgz", "svg.gz")
qt.core.plugin.factoryloader: checking directory path "D:/1a_perfect/build-testsql-Desktop_Qt_6_3_0_MinGW_64_bit-Debug/debug/iconengines" ...
qt.core.plugin.factoryloader: checking directory path "C:/Qt/6.3.0/mingw_64/plugins/imageformats" ...
qt.core.plugin.factoryloader: looking at "C:/Qt/6.3.0/mingw_64/plugins/imageformats/qgif.dll"
qt.core.plugin.loader: Found metadata in lib C:/Qt/6.3.0/mingw_64/plugins/imageformats/qgif.dll, metadata=
{
    "IID": "org.qt-project.Qt.QImageIOHandlerFactoryInterface",
    "MetaData": {
        "Keys": [
            "gif"
        ],
        "MimeTypes": [
            "image/gif"
        ]
    },
    "archlevel": 2,
    "className": "QGifPlugin",
    "debug": false,
    "version": 393984
}

qt.core.plugin.factoryloader: Got keys from plugin meta data QList("gif")
qt.core.plugin.factoryloader: looking at "C:/Qt/6.3.0/mingw_64/plugins/imageformats/qico.dll"
qt.core.plugin.loader: Found metadata in lib C:/Qt/6.3.0/mingw_64/plugins/imageformats/qico.dll, metadata=
{
    "IID": "org.qt-project.Qt.QImageIOHandlerFactoryInterface",
    "MetaData": {
        "Keys": [
            "ico",
            "cur"
        ],
        "MimeTypes": [
            "image/vnd.microsoft.icon",
            "image/vnd.microsoft.icon"
        ]
    },
    "archlevel": 2,
    "className": "QICOPlugin",
    "debug": false,
    "version": 393984
}

qt.core.plugin.factoryloader: Got keys from plugin meta data QList("ico", "cur")
qt.core.plugin.factoryloader: looking at "C:/Qt/6.3.0/mingw_64/plugins/imageformats/qjpeg.dll"
qt.core.plugin.loader: Found metadata in lib C:/Qt/6.3.0/mingw_64/plugins/imageformats/qjpeg.dll, metadata=
{
    "IID": "org.qt-project.Qt.QImageIOHandlerFactoryInterface",
    "MetaData": {
        "Keys": [
            "jpg",
            "jpeg"
        ],
        "MimeTypes": [
            "image/jpeg",
            "image/jpeg"
        ]
    },
    "archlevel": 2,
    "className": "QJpegPlugin",
    "debug": false,
    "version": 393984
}

qt.core.plugin.factoryloader: Got keys from plugin meta data QList("jpg", "jpeg")
qt.core.plugin.factoryloader: looking at "C:/Qt/6.3.0/mingw_64/plugins/imageformats/qsvg.dll"
qt.core.plugin.loader: Found metadata in lib C:/Qt/6.3.0/mingw_64/plugins/imageformats/qsvg.dll, metadata=
{
    "IID": "org.qt-project.Qt.QImageIOHandlerFactoryInterface",
    "MetaData": {
        "Keys": [
            "svg",
            "svgz"
        ],
        "MimeTypes": [
            "image/svg+xml",
            "image/svg+xml-compressed"
        ]
    },
    "archlevel": 2,
    "className": "QSvgPlugin",
    "debug": false,
    "version": 393984
}

qt.core.plugin.factoryloader: Got keys from plugin meta data QList("svg", "svgz")
qt.core.plugin.factoryloader: checking directory path "D:/1a_perfect/build-testsql-Desktop_Qt_6_3_0_MinGW_64_bit-Debug/debug/imageformats" ...
qt.core.library: "C:/Qt/6.3.0/mingw_64/plugins/imageformats/qgif.dll" loaded library
qt.core.library: "C:/Qt/6.3.0/mingw_64/plugins/imageformats/qico.dll" loaded library
qt.core.library: "C:/Qt/6.3.0/mingw_64/plugins/imageformats/qjpeg.dll" loaded library
qt.core.library: "C:/Qt/6.3.0/mingw_64/plugins/imageformats/qsvg.dll" loaded library
qt.core.plugin.factoryloader: checking directory path "C:/Qt/6.3.0/mingw_64/plugins/sqldrivers" ...
qt.core.plugin.factoryloader: looking at "C:/Qt/6.3.0/mingw_64/plugins/sqldrivers/qsqlite.dll"
qt.core.plugin.loader: Found metadata in lib C:/Qt/6.3.0/mingw_64/plugins/sqldrivers/qsqlite.dll, metadata=
{
    "IID": "org.qt-project.Qt.QSqlDriverFactoryInterface",
    "MetaData": {
        "Keys": [
            "QSQLITE"
        ]
    },
    "archlevel": 2,
    "className": "QSQLiteDriverPlugin",
    "debug": false,
    "version": 393984
}

qt.core.plugin.factoryloader: Got keys from plugin meta data QList("QSQLITE")
qt.core.plugin.factoryloader: looking at "C:/Qt/6.3.0/mingw_64/plugins/sqldrivers/qsqlmysql.dll"
qt.core.plugin.loader: Found metadata in lib C:/Qt/6.3.0/mingw_64/plugins/sqldrivers/qsqlmysql.dll, metadata=
{
    "IID": "org.qt-project.Qt.QSqlDriverFactoryInterface",
    "MetaData": {
        "Keys": [
            "QMYSQL",
            "QMARIADB"
        ]
    },
    "archlevel": 2,
    "className": "QMYSQLDriverPlugin",
    "debug": true,
    "version": 393984
}

qt.core.plugin.factoryloader: Got keys from plugin meta data QList("QMYSQL", "QMARIADB")
qt.core.plugin.factoryloader: looking at "C:/Qt/6.3.0/mingw_64/plugins/sqldrivers/qsqlodbc.dll"
qt.core.plugin.loader: Found metadata in lib C:/Qt/6.3.0/mingw_64/plugins/sqldrivers/qsqlodbc.dll, metadata=
{
    "IID": "org.qt-project.Qt.QSqlDriverFactoryInterface",
    "MetaData": {
        "Keys": [
            "QODBC"
        ]
    },
    "archlevel": 2,
    "className": "QODBCDriverPlugin",
    "debug": false,
    "version": 393984
}

qt.core.plugin.factoryloader: Got keys from plugin meta data QList("QODBC")
qt.core.plugin.factoryloader: looking at "C:/Qt/6.3.0/mingw_64/plugins/sqldrivers/qsqlpsql.dll"
qt.core.plugin.loader: Found metadata in lib C:/Qt/6.3.0/mingw_64/plugins/sqldrivers/qsqlpsql.dll, metadata=
{
    "IID": "org.qt-project.Qt.QSqlDriverFactoryInterface",
    "MetaData": {
        "Keys": [
            "QPSQL"
        ]
    },
    "archlevel": 2,
    "className": "QPSQLDriverPlugin",
    "debug": false,
    "version": 393984
}

qt.core.plugin.factoryloader: Got keys from plugin meta data QList("QPSQL")
qt.core.plugin.factoryloader: checking directory path "D:/1a_perfect/build-testsql-Desktop_Qt_6_3_0_MinGW_64_bit-Debug/debug/sqldrivers" ...
QList("QSQLITE", "QMARIADB", "QMYSQL", "QODBC", "QPSQL")
qt.core.library: "C:/Qt/6.3.0/mingw_64/plugins/sqldrivers/qsqlmysql.dll" loaded library
qt.core.plugin.factoryloader: checking directory path "C:/Qt/6.3.0/mingw_64/plugins/accessible" ...
qt.core.plugin.factoryloader: checking directory path "D:/1a_perfect/build-testsql-Desktop_Qt_6_3_0_MinGW_64_bit-Debug/debug/accessible" ...
qt.core.plugin.factoryloader: checking directory path "C:/Qt/6.3.0/mingw_64/plugins/accessiblebridge" ...
qt.core.plugin.factoryloader: checking directory path "D:/1a_perfect/build-testsql-Desktop_Qt_6_3_0_MinGW_64_bit-Debug/debug/accessiblebridge" ...

[jsulm]

@yuyu said in I had complied qsqlmysql.dll.:

qt.core.library: "C:/Qt/6.3.0/mingw_64/plugins/sqldrivers/qsqlmysql.dll" loaded library

Looks good now

[yuyu]

@jsulm I can not connect my mysql database .

[jsulm]

@yuyu What does db.open() return?
What does https://doc.qt.io/qt-5/qsqldatabase.html#lastError return after open() call?

[Nevez]

@yuyu Still getting driver not installed error? and yes share the result of db.open() as well.

[yuyu]

@jsulm false

[jsulm]

@yuyu I asked two questions. Would you be so kind to also answer the second one?

[yuyu]

@Nevez yes，but I had install it. it return false.
sometime has

qt.core.plugin.loader: QLibraryPrivate::loadPlugin failed on "C:/Qt/6.3.0/mingw_64/plugins/sqldrivers/qsqlmysql.dll" : "Cannot load library C:\\Qt\\6.3.0\\mingw_64\\plugins\\sqldrivers\\qsqlmysql.dll:

[jsulm]

@yuyu I'm confused: before you posted output showing that the plug-in was loaded.
Now you posted output showing that it could not be loaded.

Please do again what was suggested before: set QT_DEBUG_PLUGINS and if the plug-in fails to load post the output here...

[yuyu]

@jsulm you can try it ,it may be a problem,you can use mysql 8.0.28 and qt6.3 , you can find this error.

[jsulm]

@yuyu I'm not going to try anything.
I suggested what you can do to get help.
It is up to you to do that or not...

[yuyu]

@jsulm I think it's a waste of time, regardless of the problem

[Nevez]

@yuyu
I am using Mysql 8.x.x and QT 6.2.3. Mysql works fine too.
According to the error you get, you may have placed the relevant DLL in the wrong place or you may have used the wrong version DLL.
There was a video on youtube that did this well. You will find it on your first search.

[yuyu]

@Nevez said in I had complied qsqlmysql.dll.:

I am using Mysql 8.x.x and QT 6.2.3. Mysql works fine too.
According to the error you get, you may have placed the relevant DLL in the wrong place or you may have used the wrong version DLL.
There was a video on youtube that did this well. You will find it on your first search.

I user mysql >8.0.19,I see the doc, tha say