select count(*) from sqlite_master where type='table' and name='TableName'

bool bTableExist = query.exec(QString("select count(*) from sqlite_master where type='table' and name='%1'").arg(strTableName))); //关键的判断
if(bTableExist)
{
    qDebug() << "table exists";
}
else
{
    qDebug() << "table does not exist";
}

delete fromLifeCirClewhereRFIDin(selectlimit 400) //使用子查询删除表前400行数据