QT实现模糊查询时出现的BUG

小弟使用的数据库时sqlite，

上代码：//学生查询课程模块
student_chack_course::student_chack_course(QWidget *parent)
:QDialog(parent)
{
LineEdit_1=new QLineEdit;
Label_1=new QLabel(tr("请输入关键字："));
Label_1->setBuddy(LineEdit_1);
button_1=new QPushButton;
button_1->setText(tr("查询"));
button_1->setDefault(true);
button_1->setEnabled(false);
button_2=new QPushButton;
button_2->setText(tr("关闭"));
button_3=new QPushButton;
button_3->setText(tr("另存为"));

model=new QSqlRelationalTableModel;
model->setTable("course");
model->setSort(0,Qt::AscendingOrder);
model->setHeaderData(0,Qt::Horizontal,tr("课程号"));
model->setHeaderData(1,Qt::Horizontal,tr("课程名称"));
model->setHeaderData(2,Qt::Horizontal,tr("先驱课程"));
model->setHeaderData(3,Qt::Horizontal,tr("学分"));
model->setHeaderData(4,Qt::Horizontal,tr("上课地点"));
model->setHeaderData(5,Qt::Horizontal,tr("上课时间"));
model->setRelation(2,QSqlRelation("course","cno","cname"));
model->select();



view=new QTableView;
view->setModel(model);
view->setSelectionMode(QAbstractItemView::SingleSelection);
view->setSelectionBehavior(QAbstractItemView::SelectRows);
view->resizeColumnsToContents();
view->setItemDelegate(new QSqlRelationalDelegate(view));

QHeaderView *header=view->horizontalHeader();
header->setStretchLastSection(true);


connect(button_1,SIGNAL(clicked()),this,SLOT(to_record()));
connect(LineEdit_1,SIGNAL(textChanged(const QString &)),this,SLOT(enable_button(const QString &)));
connect(button_2,SIGNAL(clicked()),this,SLOT(to_close()));


QHBoxLayout *down_layout=new QHBoxLayout;
down_layout->addWidget(Label_1);
down_layout->addWidget(LineEdit_1);
down_layout->addWidget(button_1);
down_layout->addWidget(button_2);
down_layout->addWidget(button_3);
down_layout->addStretch();

QVBoxLayout *mainlayout=new QVBoxLayout;
mainlayout->addWidget(view);
mainlayout->addLayout(down_layout);
setLayout(mainlayout);
this->setFixedSize(500,400);

}
void student_chack_course::enable_button(const QString &text)//有内容输入时,查询--按钮--被--激--活
{
button_1->setEnabled(!text.isEmpty());
}

void student_chack_course::to_close()//关闭按钮实现
{
this->close();
}

void student_chack_course::to_record()//模糊匹配
{
model->setFilter(tr("cname='%1'").arg(QString("like %")+LineEdit_1->text()+QString("%")));
model->select();

}