bool a=FALSE;
QSqlDatabase* db;

void  Form0::PushButton2_clicked()
{
    QSqlDatabase *db = QSqlDatabase::database( "SqlEx" );
    QSqlQuery query( LineEdit2->text(), db );
    //query.exec();
    if (!query.isActive()) 
	query.lastError().showMessage("---");
    query.next();
    LineEdit1->setText(query.value(0).toString());
    this->setCaption(query.value(0).toString());
}

bool a=FALSE;
QSqlDatabase* db;
QSqlQuery query;

void  Form0::PushButton2_clicked()
{
    QSqlDatabase *db = QSqlDatabase::database( "SqlEx" );
    query( LineEdit2->text(), db );
    //query.exec();
    if (!query.isActive()) 
	query.lastError().showMessage("---");
    query.next();
    LineEdit1->setText(query.value(0).toString());
    this->setCaption(query.value(0).toString());
}

-----------------------------------------------------------------------------------------------------
Запущена компиляция по стеку <Стандарт>.
In file included from /usr/lib/qt-3.3.3/include/qwindowdefs.h:45,
from /usr/lib/qt-3.3.3/include/qwidget.h:42,
from /usr/lib/qt-3.3.3/include/qdesktopwidget.h:40,
from /usr/lib/qt-3.3.3/include/qapplication.h:42,
from main.cpp:4:
/usr/lib/qt-3.3.3/include/qnamespace.h:919: warning: ignoring pragma:
/usr/lib/qt-3.3.3/include/qnamespace.h:926: warning: `class QPersistant' has virtual functions but non-virtual destructor
In file included from /usr/lib/qt-3.3.3/include/qwindowdefs.h:45,
from /usr/lib/qt-3.3.3/include/qobject.h:43,
from /usr/lib/qt-3.3.3/include/qobjectlist.h:42,
from .ui/form0.h:14,
from .ui/form0.cpp:10:
/usr/lib/qt-3.3.3/include/qnamespace.h:919: warning: ignoring pragma:
/usr/lib/qt-3.3.3/include/qnamespace.h:926: warning: `class QPersistant' has virtual functions but non-virtual destructor
In file included from .ui/form0.cpp:22:
.ui/../form0.ui.h: In method `void Form0::PushButton2_clicked()':
.ui/../form0.ui.h:56: no match for call to `(QSqlQuery) (QString, QSqlDatabase *&)'
*** [.obj/form0.o] Ошибка 1
Программа завершилась с ошибкой. Время работы: 00:00:11