QSqlQuery(3qt)

NAME
QSqlQuery - Means of executing and manipulating SQL statements

SYNOPSIS
#include <qsqlquery.h>

Inherited by QSqlCursor.

  Public Members
QSqlQuery ( QSqlResult * r )
QSqlQuery ( const QString & query = QString::null, QSqlDatabase * db = 0 )
QSqlQuery ( const QSqlQuery & other )
QSqlQuery & operator= ( const QSqlQuery & other )
virtual ~QSqlQuery ()
bool isValid () const
bool isActive () const
bool isNull ( int field ) const
int at () const
QString lastQuery () const
int numRowsAffected () const
QSqlError lastError () const
bool isSelect () const
int size () const
const QSqlDriver * driver () const
const QSqlResult * result () const
virtual bool exec ( const QString & query )
virtual QVariant value ( int i ) const
virtual bool seek ( int i, bool relative = FALSE )
virtual bool next ()
virtual bool prev ()
virtual bool first ()
virtual bool last ()

  Protected Members
virtual void beforeSeek ()
virtual void afterSeek ()

DESCRIPTION
The QSqlQuery class provides a means of executing and manipulating SQL statements.

QSqlQuery encapsulates the functionality involved in creating, navigating and retrieving data from SQL queries which are executed on a QSqlDatabase. It can be used to execute DML (data manipulation language) statements, e.g. SELECT, INSERT, UPDATE and DELETE, and also DDL (data definition language) statements, e.g. CREATE TABLE. It can also be used to execute database-specific commands which are not standard SQL (e.g. SET DATESTYLE=ISO for PostgreSQL).

Successfully executed SQL statements set the query to an active state (isActive() returns TRUE) otherwise the query is set to an inactive state. In either case, when executing a new SQL statement, the query is positioned on an invalid record; an active query must be navigated to a valid record (so that isValid() returns TRUE) before values can be retrieved.

Navigating records is performed with the following functions:

next()

prev()

first()

last()

seek(int)

These functions allow the programmer to move forward, backward or arbitrarily through the records returned by the query. Once an active query is positioned on a valid record, data can be retrieved using value(). All data is transferred from the SQL backend using QVariants.

For example:

    QSqlQuery query( "select name from customer" );
    while ( query.next() ) {
        QString name = query.value(0).toString();
        doSomething( name );
    }

To access the data returned by a query, use the value() method. Each field in the data returned by a SELECT statement is accessed by passing the index number of the desired field, starting with 0. There are no methods to access a field by name to make sure the usage of QSqlQuery is as optimal as possible (see QSqlCursor for a more flexible interface for selecting data from a table or view in the database).

See also QSqlDatabase, QSqlCursor, QVariant and Database Classes.

MEMBER FUNCTION DOCUMENTATION

QSqlQuery::QSqlQuery ( QSqlResult * r )
Creates a QSqlQuery object which uses the QSqlResult r to communicate with a database.

QSqlQuery::QSqlQuery ( const QString & query = QString::null, QSqlDatabase * db = 0 )
Creates a QSqlQuery object using the SQL query and the database db. If db is 0, (the default), the application's default database is used.

See also QSqlDatabase.

QSqlQuery::QSqlQuery ( const QSqlQuery & other )
Constructs a copy of other.

QSqlQuery::~QSqlQuery () [virtual]
Destroys the object and frees any allocated resources.

void QSqlQuery::afterSeek () [virtual protected]
Protected virtual function called after the internal record pointer is moved to a new record. The default implementation does nothing.

int QSqlQuery::at () const
Returns the current internal position of the query. The first record is at position zero. If the position is invalid, a QSql::Location will be returned indicating the invalid position.

See also isValid().

Example: sql/overview/navigating/main.cpp.

void QSqlQuery::beforeSeek () [virtual protected]
Protected virtual function called before the internal record pointer is moved to a new record. The default implementation does nothing.

const QSqlDriver * QSqlQuery::driver () const
Returns a pointer to the database driver associated with the query.

bool QSqlQuery::exec ( const QString & query ) [virtual]
Executes the SQL query. Returns TRUE if the query was successful sets the query state to active, otherwise returns FALSE and the query becomes inactive. The query string must use syntax appropriate for the SQL database being queried, for example, standard SQL.

After the query is executed, the query is positioned on an invalid record, and must be navigated to a valid record before data values can be retrieved.

See also isActive(), isValid(), next(), prev(), first(), last() and seek().

Examples:

bool QSqlQuery::first () [virtual]
Retrieves the first record in the result, if available, and positions the query on the retrieved record. Note that the result must be in an active state and isSelect() must return TRUE before calling this function or it will do nothing and return FALSE. Returns TRUE if successful. If unsuccessful the query position is set to an invalid position and FALSE is returned.

Example: sql/overview/navigating/main.cpp.

bool QSqlQuery::isActive () const
Returns TRUE if the query is currently active, otherwise returns FALSE.

Examples:

bool QSqlQuery::isNull ( int field ) const
Returns TRUE if field is currently NULL, otherwise returns FALSE. The query must be active and positioned on a valid record before calling this function otherwise it returns FALSE. Note that, for some drivers, isNull() will not return accurate information until after an attempt is made to retrieve data.

See also isActive(), isValid() and value().

bool QSqlQuery::isSelect () const
Returns TRUE if the current query is a SELECT statement, otherwise returns FALSE.

bool QSqlQuery::isValid () const
Returns TRUE if the query is currently positioned on a valid record, otherwise returns FALSE.

bool QSqlQuery::last () [virtual]
Retrieves the last record in the result, if available, and positions the query on the retrieved record. Note that the result must be in an active state and isSelect() must return TRUE before calling this function or it will do nothing and return FALSE. Returns TRUE if successful. If unsuccessful the query position is set to an invalid position and FALSE is returned.

Example: sql/overview/navigating/main.cpp.

QSqlError QSqlQuery::lastError () const
Returns error information about the last error (if any) that occurred.

See also QSqlError.

QString QSqlQuery::lastQuery () const
Returns the text of the current query being used, or QString::null if there is no current query text.

bool QSqlQuery::next () [virtual]
Retrieves the next record in the result, if available, and positions the query on the retrieved record. Note that the result must be in an active state and isSelect() must return TRUE before calling this function or it will do nothing and return FALSE.

The following rules apply:

If the result is currently located before the first record, e.g. immediately after a query is executed, an attempt is made to retrieve the first record.

If the result is currently located after the last record, there is no change and FALSE is returned.

If the result is located somewhere in the middle, an attempt is made to retrieve the next record.

If the record could not be retrieved, the result is positioned after the last record and FALSE is returned. If the record is successfully retrieved, TRUE is returned.

See also at() and isValid().

Examples:

int QSqlQuery::numRowsAffected () const
Returns the number of rows affected by the result's SQL statement, or -1 if it cannot be determined. Note that for SELECT statements, this value will be the same as size(). If the query is not active (isActive() returns FALSE), -1 is returned.

See also size() and QSqlDriver::hasFeature().

Examples:

QSqlQuery & QSqlQuery::operator= ( const QSqlQuery & other )
Assigns other to the query.

bool QSqlQuery::prev () [virtual]
Retrieves the previous record in the result, if available, and positions the query on the retrieved record. Note that the result must be in an active state and isSelect() must return TRUE before calling this function or it will do nothing and return FALSE.

The following rules apply:

If the result is currently located before the first record, there is no change and FALSE is returned.

If the result is currently located after the last record, an attempt is made to retrieve the last record.

If the result is somewhere in the middle, an attempt is made to retrieve the previous record.

If the record could not be retrieved, the result is positioned before the first record and FALSE is returned. If the record is successfully retrieved, TRUE is returned.

See also at().

const QSqlResult * QSqlQuery::result () const
Returns a pointer to the result associated with the query.

bool QSqlQuery::seek ( int i, bool relative = FALSE ) [virtual]
Retrieves the record at position (or offset) i, if available, and positions the query on the retrieved record. The first record is at position zero. Note that the query must be in an active state and isSelect() must return TRUE before calling this function.

The following rules apply:

If relative is FALSE (the default), the following rules apply:

If i is negative, the result is positioned before the first record and FALSE is returned.

Otherwise, an attempt is made to move to the record at position i. If the record at position i could not be retrieved, the result is positioned after the last record and FALSE is returned. If the record is successfully retrieved, TRUE is returned.

If relative is TRUE, the following rules apply:

If the result is currently positioned before the first record or on the first record, and i is negative, there is no change, and FALSE is returned.

If the result is currently located after the last record, and i is positive, there is no change, and FALSE is returned.

If the result is currently located somewhere in the middle, and the relative offset i moves the result below zero, the result is positioned before the first record and FALSE is returned.

Otherwise, an attempt is made to move to the record i records ahead of the current record (or i records behind the current record if i is negative). If the record at offset i could not be retrieved, the result is positioned after the last record if i >= 0, (or before the first record if i is negative), and FALSE is returned. If the record is successfully retrieved, TRUE is returned.

Example: sql/overview/navigating/main.cpp.

int QSqlQuery::size () const
Returns the size of the result, (number of rows returned), or -1 if the size cannot be determined or the database does not support reporting information about query sizes. Note that for non-SELECT statements (isSelect() returns FALSE), size() will return -1. If the query is not active (isActive() returns FALSE), -1 is returned.

To determine the number of rows affected by a non-SELECT statement, use numRowsAffected().

See also isActive(), numRowsAffected() and QSqlDriver::hasFeature().

Example: sql/overview/navigating/main.cpp.

QVariant QSqlQuery::value ( int i ) const [virtual]
Returns the value of field i (zero based).

The fields are numbered from left to right using the text of the SELECT statement, e.g. in "select forename, surname from people", field 0 is forename and field 1 is surname. Using SELECT * is not recommended because the order of the fields in the query is undefined.

An invalid QVariant is returned if field i does not exist, if the query is inactive, or if the query is positioned on an invalid record.

See also prev(), next(), first(), last(), seek(), isActive() and isValid().

Examples:

SEE ALSO
http://doc.trolltech.com/qsqlquery.html http://www.trolltech.com/faq/tech.html

COPYRIGHT
Copyright 1992-2001 Trolltech AS, http://www.trolltech.com. See the license file included in the distribution for a complete license statement.

AUTHOR
Generated automatically from the source code.

BUGS
If you find a bug in Qt, please report it as described in http://doc.trolltech.com/bughowto.html. Good bug reports help us to help you. Thank you.

The definitive Qt documentation is provided in HTML format; it is located at $QTDIR/doc/html and can be read using Qt Assistant or with a web browser. This man page is provided as a convenience for those users who prefer man pages, although this format is not officially supported by Trolltech.

If you find errors in this manual page, please report them to qt-bugs@trolltech.com. Please include the name of the manual page (qsqlquery.3qt) and the Qt version (3.0.3).