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Set environment variable QT_DEBUG_PLUGINS=1 before running your program, then run it. This gives diagnostic output, look through it to see why it fails to load QMYSQL driver. 在运行程序之前设置环境变量“QT_DEBUG_PLUGINS=1”，然后运行它。 这会提供诊断输出，查看它以了解为什么无法加载“QMYSQL”驱动程序。

@Feng-chunX database is locked => "happens only when there is another connection with an active transaction" You have another process or another thread which is writing to the database? Google: qsqlquery "database is locked"

忘記附上我使用的QT版本是5.15.14.

@Lee_Corl said in I didn't create a toolBar, why does it appear? How can I delete the toolBar?: @SGaist I dont use it What do you mean ?

当然不行，QWidget及其子类只能在主线程中创建运行。

@JonB Finally, I chose Qt under Linux, which is convenient for Windows installation environment. Thank you

Set environment variable QT_DEBUG_PLUGINS to 1 and re-run.

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