return QSqlIndex();}/*!    Returns a QSqlRecord populated with the names of the fields in    table \a tableName. If no such table exists, an empty record is    returned. The default implementation returns an empty record.*/QSqlRecord QSqlDriver::record(const QString & /* tableName */) const{    return QSqlRecord();}/*!    Returns the \a identifier escaped according to the database rules.    \a identifier can either be a table name or field name, dependent    on \a type.    The default implementation does nothing. */QString QSqlDriver::escapeIdentifier(const QString &identifier, IdentifierType) const{    return identifier;}/*!    Returns a SQL statement of type \a type for the table \a tableName    with the values from \a rec. If \a preparedStatement is true, the    string will contain placeholders instead of values.    This method can be used to manipulate tables without having to worry    about database-dependent SQL dialects. For non-prepared statements,    the values will be properly escaped.*/QString QSqlDriver::sqlStatement(StatementType type, const QString &tableName,                                 const QSqlRecord &rec, bool preparedStatement) const{    int i;    QString s;    s.reserve(128);    switch (type) {    case SelectStatement:        for (i = 0; i < rec.count(); ++i) {            if (rec.isGenerated(i))                s.append(escapeIdentifier(rec.fieldName(i), FieldName)).append(QLatin1String(", "));        }        if (s.isEmpty())            return s;        s.chop(2);        s.prepend(QLatin1String("SELECT ")).append(QLatin1String(" FROM ")).append(                escapeIdentifier(tableName, TableName));        break;    case WhereStatement:        if (preparedStatement) {            for (int i = 0; i < rec.count(); ++i)                s.append(escapeIdentifier(rec.fieldName(i), FieldName)).append(                         QLatin1String(" = ? AND "));        } else {            for (i = 0; i < rec.count(); ++i) {                s.append(escapeIdentifier(rec.fieldName(i), FieldName));                QString val = formatValue(rec.field(i));                if (val == QLatin1String("NULL"))                    s.append(QLatin1String(" IS NULL"));                else                    s.append(QLatin1String(" = ")).append(val);                s.append(QLatin1String(" AND "));            }        }        if (!s.isEmpty()) {            s.prepend(QLatin1String("WHERE "));            s.chop(5); // remove tailing AND        }        break;    case UpdateStatement:        s.append(QLatin1String("UPDATE ")).append(escapeIdentifier(tableName, TableName)).append(                 QLatin1String(" SET "));        for (i = 0; i < rec.count(); ++i) {            if (!rec.isGenerated(i) || !rec.value(i).isValid())                continue;            s.append(escapeIdentifier(rec.fieldName(i), FieldName)).append(QLatin1Char('='));            if (preparedStatement)                s.append(QLatin1Char('?'));            else                s.append(formatValue(rec.field(i)));            s.append(QLatin1String(", "));        }        if (s.endsWith(QLatin1String(", ")))            s.chop(2);        else            s = QString();        break;    case DeleteStatement:        s.append(QLatin1String("DELETE FROM ")).append(escapeIdentifier(tableName, TableName));        break;    case InsertStatement: {        s.append(QLatin1String("INSERT INTO ")).append(escapeIdentifier(                    tableName, TableName)).append(QLatin1String(" ("));        QString vals;        for (i = 0; i < rec.count(); ++i) {            if (!rec.isGenerated(i) || !rec.value(i).isValid())                continue;            s.append(escapeIdentifier(rec.fieldName(i), FieldName)).append(QLatin1String(", "));            if (preparedStatement)                vals.append(QLatin1String("?"));            else                vals.append(formatValue(rec.field(i)));            vals.append(QLatin1String(", "));        }        if (vals.isEmpty()) {            s = QString();        } else {            vals.chop(2); // remove trailing comma            s[s.length() - 2] = QLatin1Char(')');            s.append(QLatin1String("VALUES (")).append(vals).append(QLatin1String(")"));        }        break; }    }    return s;}/*!    Returns a string representation of the \a field value for the    database. This is used, for example, when constructing INSERT and    UPDATE statements.    The default implementation returns the value formatted as a string    according to the following rules:    \list    \i If \a field is character data, the value is returned enclosed    in single quotation marks, which is appropriate for many SQL    databases. Any embedded single-quote characters are escaped    (replaced with two single-quote characters). If \a trimStrings is    true (the default is false), all trailing whitespace is trimmed    from the field.    \i If \a field is date/time data, the value is formatted in ISO    format and enclosed in single quotation marks. If the date/time    data is invalid, "NULL" is returned.    \i If \a field is \link QByteArray bytearray\endlink data, and the    driver can edit binary fields, the value is formatted as a    hexadecimal string.    \i For any other field type, toString() is called on its value    and the result of this is returned.    \endlist    \sa QVariant::toString()*/QString QSqlDriver::formatValue(const QSqlField &field, bool trimStrings) const{    const QLatin1String nullTxt("NULL");    QString r;    if (field.isNull())        r = nullTxt;    else {        switch (field.type()) {        case QVariant::Int:        case QVariant::UInt:            if (field.value().type() == QVariant::Bool)                r = field.value().toBool() ? QLatin1String("1") : QLatin1String("0");            else                r = field.value().toString();            break;#ifndef QT_NO_DATESTRING	case QVariant::Date:            if (field.value().toDate().isValid())                r = QLatin1Char('\'') + field.value().toDate().toString(Qt::ISODate)                    + QLatin1Char('\'');            else                r = nullTxt;            break;        case QVariant::Time:            if (field.value().toTime().isValid())                r =  QLatin1Char('\'') + field.value().toTime().toString(Qt::ISODate)                     + QLatin1Char('\'');            else                r = nullTxt;            break;        case QVariant::DateTime:            if (field.value().toDateTime().isValid())                r = QLatin1Char('\'') +                    field.value().toDateTime().toString(Qt::ISODate) + QLatin1Char('\'');            else                r = nullTxt;            break;#endif        case QVariant::String:        case QVariant::Char:        {            QString result = field.value().toString();            if (trimStrings) {                int end = result.length() - 1;                while (end && result.at(end).isSpace()) /* skip white space from end */                    end--;                result.truncate(end);            }            /* escape the "'" character */            result.replace(QLatin1Char('\''), QLatin1String("''"));            r = QLatin1Char('\'') + result + QLatin1Char('\'');            break;        }        case QVariant::Bool:            if (field.value().toBool())                r = QLatin1String("1");            else                r = QLatin1String("0");            break;        case QVariant::ByteArray : {            if (hasFeature(BLOB)) {                QByteArray ba = field.value().toByteArray();                QString res;                static const char hexchars[] = "0123456789abcdef";                for (int i = 0; i < ba.size(); ++i) {                    uchar s = (uchar) ba[i];                    res += QLatin1Char(hexchars[s >> 4]);                    res += QLatin1Char(hexchars[s & 0x0f]);                }                r = QLatin1Char('\'') + res +  QLatin1Char('\'');                break;            }        }        default:            r = field.value().toString();            break;        }    }    return r;}/*!    Returns the low-level database handle wrapped in a QVariant or an    invalid variant if there is no handle.    \warning Use this with uttermost care and only if you know what you're doing.    \warning The handle returned here can become a stale pointer if the connection    is modified (for example, if you close the connection).    \warning The handle can be NULL if the connection is not open yet.    The handle returned here is database-dependent, you should query the type    name of the variant before accessing it.    This example retrieves the handle for a connection to sqlite:    \code    QSqlDatabase db = ...;    QVariant v = db.driver()->handle();    if (v.isValid() && v.typeName() == "sqlite3*") {        // v.data() returns a pointer to the handle        sqlite3 *handle = *static_cast<sqlite3 **>(v.data());        if (handle != 0) { // check that it is not NULL            ...        }    }    \endcode    This snippet returns the handle for PostgreSQL or MySQL:    \code    if (v.typeName() == "PGconn*") {        PGconn *handle = *static_cast<PGconn **>(v.data());        if (handle != 0) ...    }    if (v.typeName() == "MYSQL*") {        MYSQL *handle = *static_cast<MYSQL **>(v.data());        if (handle != 0) ...    }    \endcode    \sa QSqlResult::handle()*/QVariant QSqlDriver::handle() const{    return QVariant();}/*!    \fn QSqlRecord QSqlDriver::record(const QSqlQuery& query) const    Use query.record() instead.*//*!    \fn QSqlRecord QSqlDriver::recordInfo(const QString& tablename) const    Use record() instead.*//*!    \fn QSqlRecord QSqlDriver::recordInfo(const QSqlQuery& query) const    Use query.record() instead.*//*!    \fn QString QSqlDriver::nullText() const    sqlStatement() is now used to generate SQL. Use tr("NULL") for example, instead.*//*!    \fn QString QSqlDriver::formatValue(const QSqlField *field, bool trimStrings) const    Use the other formatValue() overload instead.*/