和原来的代码写到一起，给我一个能运行的完整代码

为了保持代码的完整性，以下是将异常处理合并到原有代码中的版本。请注意，我已经把异常处理添加到了`db_connect`和`sql_exec`方法中：

import sys
from PyQt5.QtCore import Qt
from PyQt5.QtSql import QSqlDatabase, QSqlTableModel, QSqlQuery
from PyQt5.QtWidgets import QApplication, QWidget, QMessageBox, QTableView
from ui.DBDialog import *
from PyQt5.QtGui import QMessageBox

class DBDemo(Ui_Dialog, QTableView):
    def __init__(self):
        super(DBDemo, self).__init__()
        self.setupUi(self)
        self.btnCancel.clicked.connect(self.close)
        self.db = None
        self.db_connect()
        self.sql_exec()

    def db_connect(self):
        try:
            self.db = QSqlDatabase.addDatabase('QSQLITE')
            self.db.setDatabaseName('./example.db')
            if not self.db.open():
                QMessageBox.critical(self, 'Database Connection', self.db.lastError().text())
        except QSqlError as e:
            QMessageBox.critical(self, 'Database Error', str(e))

    def closeEvent(self, QCloseEvent):
        if self.db is not None:
            self.db.close()

    def sql_exec(self):
        try:
            self.model = QSqlTableModel(self)
            self.model.setTable('users')
            self.model.setEditStrategy(QSqlTableModel.OnFieldChange)
            self.model.setHeaderData(0, Qt.Horizontal, 'id')
            self.model.setHeaderData(1, Qt.Horizontal, 'name')
            self.model.setHeaderData(2, Qt.Horizontal, 'age')

            self.model.select()

            self.tableView.setModel(self.model)

            self.tableView.setSelectionBehavior(QTableView.SelectRows)
            self.btnDelete.clicked.connect(self.deleteRow)
        except QSqlError as e:
            QMessageBox.warning(self, 'SQL Execution Error', str(e))

    def deleteRow(self):
        index = self.tableView.currentIndex()
        if index.isValid():
            row = index.row()
            id = self.model.record(row).value('id')
            name = self.model.record(row).value('name')
            age = self.model.record(row).value('age')
            msg = f"是否删除选定的【{id}-{name}-{age}】"
            reply = QMessageBox.question(self, "删除", msg, QMessageBox.Yes | QMessageBox.No, QMessageBox.No)
            if reply == QMessageBox.Yes:
                self.model.removeRow(row)
                self.model.submitAll()

                self.model.select()
                self.tableView.setModel(self.model)

if __name__ == '__main__':
    app = QApplication(sys.argv)
    demo = DBDemo()
    demo.show()

现在，如果你的环境配置正确并且example.db文件存在，这段代码应该能正确地建立数据库连接，执行SQL查询，并处理可能出现的错误，避免程序因异常而终止。