@rezaMSLM
Because your folder name has spaces in it, when you changed the command line you don't seem to have done the necessary quoting? Does the following work better:

qmake -- "MYSQL_INCDIR=C:\Program Files\MySQL\MySQL Server 5.7/include" "MYSQL_LIBDIR=C:\Program Files\MySQL\MySQL Server 5.7/lib/opt"

Otherwise, although it may be OK, you are mixing \s and /s in your version, is that an issue?

I Tried both

qmake -- MYSQL_INCDIR=C:\Program Files\MySQL\MySQL Server 5.7/include "MYSQL_LIBDIR=C:\Program Files\MySQL\MySQL Server 5.7/lib/opt"

and

qmake -- "MYSQL_INCDIR=C:/Program Files/MySQL/MySQL Server 5.7/include" "MYSQL_LIBDIR=C:/Program Files/MySQL/MySQL Server 5.7/lib/opt"

but receive the same error:

D:\Qt\Qt5.9.6\5.9.6\Src\qtbase\src\plugins\sqldrivers\qtsqldrivers-config.pri: the system cannot find the file specified.
project ERROR: Library 'mysql' is not defined.

EDIT:

I have no folder named "opt" in "C:/Program Files/MySQL/MySQL Server 5.7/lib"
my mysql.h file is in

C:\Program Files\MySQL\MySQL Server 5.7\include

and libmysql.lib is in

C:\Program Files\MySQL\MySQL Server 5.7\lib

so I used this code:

qmake -- "MYSQL_INCDIR=C:/Program Files/MySQL/MySQL Server 5.7/include" "MYSQL_LIBDIR=C:/Program Files/MySQL/MySQL Server 5.7/lib"

but have the same error

qmake -- "MYSQL_INCDIR=C:\Program Files\MySQL\MySQL Server 5.7/include" "MYSQL_LIBDIR=C:\Program Files\MySQL\MySQL Server 5.7/lib/opt"

Otherwise, although it may be OK, you are mixing \s and /s in your version, is that an issue?

cd %QTDIR%\qtbase\src\plugins\sqldrivers
qmake -- MYSQL_INCDIR=C:/MySQL/include "MYSQL_LIBDIR=C:/MYSQL/MySQL Server <version>/lib/opt"
nmake sub-mysql

my MySQL folder location is : C:\Program Files\MySQL
so i use this code:
qmake -- MYSQL_INCDIR=C:\Program Files\MySQL\MySQL Server 5.7/include "MYSQL_LIBDIR=C:\Program Files\MySQL\MySQL Server 5.7/lib/opt"
but I Receive this error:

library mysql not defined

When you download Qt you have also the source that are provided with it.

In my case, it is in : C:\Qt\5.9\Src\qtbase\src\plugins\sqldrivers\mysql Here you have a *.pro (that is a kind of makefile generator). You just have to open it with QtCreator, Compile it and you will get a dll. This dll is the MySQL driver and must be in the same dirent of your application.

but when i want to compile the file I receive this error:

 Library 'mysql' is not defined.

Do you have mysql plugin under plugins/sqldriver directory ?

is it a *.dll file?if yes , No thereis not any *.dll file in that directory