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

#include <qsqlquery.h>

Collaboration diagram for QSqlQuery:

Public Types
enum	BatchExecutionMode { ValuesAsRows , ValuesAsColumns }
	\value ValuesAsRows - Updates multiple rows. More...

Public Member Functions
	QSqlQuery (QSqlResult *r)
	Constructs a QSqlQuery object which uses the QSqlResult result to communicate with a database.

	QSqlQuery (const QString &query=QString(), const QSqlDatabase &db=QSqlDatabase())
	Constructs a QSqlQuery object using the SQL query and the database db.

	QSqlQuery (const QSqlDatabase &db)
	Constructs a QSqlQuery object using the database db.

	QSqlQuery (const QSqlQuery &other)=delete

QSqlQuery &	operator= (const QSqlQuery &other)=delete

	QSqlQuery (QSqlQuery &&other) noexcept

	~QSqlQuery ()
	Destroys the object and frees any allocated resources.

void	swap (QSqlQuery &other) noexcept

bool	isValid () const
	Returns `true` if the query is currently positioned on a valid record; otherwise returns `false`.

bool	isActive () const
	Returns `true` if the query is {active}.

bool	isNull (int field) const
	Returns `true` if the query is not \l{isActive()}{active}, the query is not positioned on a valid record, there is no such field, or the field is null; otherwise `false`.

bool	isNull (QAnyStringView name) const
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.Returns `true` if there is no field with this name; otherwise returns isNull(int index) for the corresponding field index.

int	at () const
	Returns the current internal position of the query.

QString	lastQuery () const
	Returns the text of the current query being used, or an empty string if there is no current query text.

int	numRowsAffected () const
	Returns the number of rows affected by the result's SQL statement, or -1 if it cannot be determined.

QSqlError	lastError () const
	Returns error information about the last error (if any) that occurred with this query.

bool	isSelect () const
	Returns `true` if the current query is a `SELECT` statement; otherwise returns `false`.

int	size () const
	Returns the size of the result (number of rows returned), or -1 if the size cannot be determined or if the database does not support reporting information about query sizes.

const QSqlDriver *	driver () const
	Returns the database driver associated with the query.

const QSqlResult *	result () const
	Returns the result associated with the query.

bool	isForwardOnly () const
	Returns \l forwardOnly.

QSqlRecord	record () const
	Returns a QSqlRecord containing the field information for the current query.

void	setForwardOnly (bool forward)
	Sets \l forwardOnly to forward.

bool	exec (const QString &query)
	Executes the SQL in query.

QVariant	value (int i) const
	Returns the value of field index in the current record.

QVariant	value (QAnyStringView name) const
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.Returns the value of the field called name in the current record.

void	setNumericalPrecisionPolicy (QSql::NumericalPrecisionPolicy precisionPolicy)
	Sets \l numericalPrecisionPolicy to precisionPolicy.

QSql::NumericalPrecisionPolicy	numericalPrecisionPolicy () const
	Returns the \l numericalPrecisionPolicy.

void	setPositionalBindingEnabled (bool enable)
	Sets \l positionalBindingEnabled to enable.

bool	isPositionalBindingEnabled () const
	Returns \l positionalBindingEnabled.

bool	seek (int i, bool relative=false)
	Retrieves the record at position index, if available, and positions the query on the retrieved record.

bool	next ()
	Retrieves the next record in the result, if available, and positions the query on the retrieved record.

bool	previous ()
	Retrieves the previous record in the result, if available, and positions the query on the retrieved record.

bool	first ()
	Retrieves the first record in the result, if available, and positions the query on the retrieved record.

bool	last ()
	Retrieves the last record in the result, if available, and positions the query on the retrieved record.

void	clear ()
	Clears the result set and releases any resources held by the query.

bool	exec ()
	Executes a previously prepared SQL query.

bool	execBatch (BatchExecutionMode mode=ValuesAsRows)
	Executes a previously prepared SQL query in a batch.

bool	prepare (const QString &query)
	Prepares the SQL query query for execution.

void	bindValue (const QString &placeholder, const QVariant &val, QSql::ParamType type=QSql::In)
	Set the placeholder placeholder to be bound to value val in the prepared statement.

void	bindValue (int pos, const QVariant &val, QSql::ParamType type=QSql::In)
	Set the placeholder in position pos to be bound to value val in the prepared statement.

void	addBindValue (const QVariant &val, QSql::ParamType type=QSql::In)
	Adds the value val to the list of values when using positional value binding.

QVariant	boundValue (const QString &placeholder) const
	Returns the value for the placeholder.

QVariant	boundValue (int pos) const
	Returns the value for the placeholder at position pos.

QVariantList	boundValues () const

QStringList	boundValueNames () const

QString	boundValueName (int pos) const

QString	executedQuery () const
	Returns the last query that was successfully executed.

QVariant	lastInsertId () const
	Returns the object ID of the most recent inserted row if the database supports it.

void	finish ()
	Instruct the database driver that no more data will be fetched from this query until it is re-executed.

bool	nextResult ()
	Discards the current result set and navigates to the next if available.

Properties
bool	forwardOnly

bool	positionalBindingEnabled

QSql::NumericalPrecisionPolicy	numericalPrecisionPolicy

Detailed Description

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

\inmodule QtSql

QSqlQuery encapsulates the functionality involved in creating, navigating and retrieving data from SQL queries which are executed on a \l QSqlDatabase. It can be used to execute DML (data manipulation language) statements, such as SELECT, INSERT, UPDATE and DELETE, as well as DDL (data definition language) statements, such as {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's state to active so that isActive() returns true. Otherwise the query's state is set to inactive. 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.

For some databases, if an active query that is a {SELECT} statement exists when you call \l{QSqlDatabase::}{commit()} or \l{QSqlDatabase::}{rollback()}, the commit or rollback will fail. See isActive() for details.

\target QSqlQuery examples

Navigating records is performed with the following functions:

\list

next()
previous()
first()
last()
seek() \endlist

These functions allow the programmer to move forward, backward or arbitrarily through the records returned by the query. If you only need to move forward through the results (e.g., by using next()), you can use setForwardOnly(), which will save a significant amount of memory overhead and improve performance on some databases. 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 country FROM artist");
    while (query.next()) {
        QString country = query.value(0).toString();
        doSomething(country);
    }

To access the data returned by a query, use value(int). Each field in the data returned by a SELECT statement is accessed by passing the field's position in the statement, starting from

This makes using {SELECT *} queries inadvisable because the order of the fields returned is indeterminate.

For the sake of efficiency, there are no functions to access a field by name (unless you use prepared queries with names, as explained below). To convert a field name into an index, use record().\l{QSqlRecord::indexOf()}{indexOf()}, for example:

    QSqlQuery query("SELECT * FROM artist");
    int fieldNo = query.record().indexOf("country");
    while (query.next()) {
        QString country = query.value(fieldNo).toString();
        doSomething(country);
    }

QSqlQuery supports prepared query execution and the binding of parameter values to placeholders. Some databases don't support these features, so for those, Qt emulates the required functionality. For example, the Oracle and ODBC drivers have proper prepared query support, and Qt makes use of it; but for databases that don't have this support, Qt implements the feature itself, e.g. by replacing placeholders with actual values when a query is executed. Use numRowsAffected() to find out how many rows were affected by a non-SELECT query, and size() to find how many were retrieved by a SELECT.

Oracle databases identify placeholders by using a colon-name syntax, e.g {:name}. ODBC simply uses ? characters. Qt supports both syntaxes, with the restriction that you can't mix them in the same query.

You can retrieve the values of all the fields in a single variable using boundValues().

Note: Not all SQL operations support binding values. Refer to your database system's documentation to check their availability.

Definition at line 23 of file qsqlquery.h.

Member Enumeration Documentation

◆ BatchExecutionMode

enum QSqlQuery::BatchExecutionMode

\value ValuesAsRows - Updates multiple rows.

Treats every entry in a QVariantList as a value for updating the next row. \value ValuesAsColumns - Updates a single row. Treats every entry in a QVariantList as a single value of an array type.

Enumerator
ValuesAsRows
ValuesAsColumns

Definition at line 97 of file qsqlquery.h.

Constructor & Destructor Documentation

◆ QSqlQuery() [1/5]

QSqlQuery::QSqlQuery ( QSqlResult * r )

explicit

Constructs a QSqlQuery object which uses the QSqlResult result to communicate with a database.

Definition at line 204 of file qsqlquery.cpp.

◆ QSqlQuery() [2/5]

QSqlQuery::QSqlQuery	(	const QString &	query = QString(),
		const QSqlDatabase &	db = QSqlDatabase() )

explicit

Constructs a QSqlQuery object using the SQL query and the database db.

If db is not specified, or is invalid, the application's default database is used. If query is not an empty string, it will be executed.

See also: QSqlDatabase

Definition at line 296 of file qsqlquery.cpp.

◆ QSqlQuery() [3/5]

QSqlQuery::QSqlQuery ( const QSqlDatabase & db )

explicit

Constructs a QSqlQuery object using the database db.

If db is invalid, the application's default database will be used.

See also: QSqlDatabase

Definition at line 309 of file qsqlquery.cpp.

◆ QSqlQuery() [4/5]

QSqlQuery::QSqlQuery ( const QSqlQuery & other )

delete

◆ QSqlQuery() [5/5]

QSqlQuery::QSqlQuery ( QSqlQuery && other )

inlinenoexcept

Since: 6.2 Move-constructs a QSqlQuery from other.

Definition at line 45 of file qsqlquery.h.

◆ ~QSqlQuery()

QSqlQuery::~QSqlQuery ( )

Destroys the object and frees any allocated resources.

Definition at line 213 of file qsqlquery.cpp.

Member Function Documentation

◆ addBindValue()

void QSqlQuery::addBindValue	(	const QVariant &	val,
		QSql::ParamType	paramType = QSql::In )

Adds the value val to the list of values when using positional value binding.

The order of the addBindValue() calls determines which placeholder a value will be bound to in the prepared query. If paramType is QSql::Out or QSql::InOut, the placeholder will be overwritten with data from the database after the exec() call.

To bind a NULL value, use a null QVariant; for example, use {QVariant(QMetaType::fromType<QString>())} if you are binding a string.

See also: bindValue(), prepare(), exec(), boundValue(), boundValues()

Definition at line 1137 of file qsqlquery.cpp.

◆ at()

int QSqlQuery::at ( ) const

Returns the current internal position of the query.

The first record is at position zero. If the position is invalid, the function returns QSql::BeforeFirstRow or QSql::AfterLastRow, which are special negative values.

See also: previous(), next(), first(), last(), seek(), isActive(), isValid()

Definition at line 475 of file qsqlquery.cpp.

◆ bindValue() [1/2]

void QSqlQuery::bindValue	(	const QString &	placeholder,
		const QVariant &	val,
		QSql::ParamType	paramType = QSql::In )

Set the placeholder placeholder to be bound to value val in the prepared statement.

Note that the placeholder mark (e.g {:}) must be included when specifying the placeholder name. If paramType is QSql::Out or QSql::InOut, the placeholder will be overwritten with data from the database after the exec() call. In this case, sufficient space must be pre-allocated to store the result into.

To bind a NULL value, use a null QVariant; for example, use {QVariant(QMetaType::fromType<QString>())} if you are binding a string.

See also: addBindValue(), prepare(), exec(), boundValue(), boundValues()

Definition at line 1107 of file qsqlquery.cpp.

◆ bindValue() [2/2]

void QSqlQuery::bindValue	(	int	pos,
		const QVariant &	val,
		QSql::ParamType	paramType = QSql::In )

Set the placeholder in position pos to be bound to value val in the prepared statement.

Field numbering starts at 0. If paramType is QSql::Out or QSql::InOut, the placeholder will be overwritten with data from the database after the exec() call.

Definition at line 1120 of file qsqlquery.cpp.

◆ boundValue() [1/2]

QVariant QSqlQuery::boundValue ( const QString & placeholder ) const

Returns the value for the placeholder.

See also: boundValues(), bindValue(), addBindValue()

Definition at line 1147 of file qsqlquery.cpp.

◆ boundValue() [2/2]

QVariant QSqlQuery::boundValue ( int pos ) const

Returns the value for the placeholder at position pos.

See also: boundValues()

Definition at line 1156 of file qsqlquery.cpp.

◆ boundValueName()

QString QSqlQuery::boundValueName ( int pos ) const

Since: 6.6

Returns the bound value name at position pos.

The order of the list is in binding order, irrespective of whether named or positional binding is used.

See also: boundValueNames()

Definition at line 1207 of file qsqlquery.cpp.

◆ boundValueNames()

QStringList QSqlQuery::boundValueNames ( ) const

Since: 6.6

Returns the names of all bound values.

The order of the list is in binding order, irrespective of whether named or positional binding is used.

See also: boundValues(), boundValueName()

Definition at line 1192 of file qsqlquery.cpp.

◆ boundValues()

QVariantList QSqlQuery::boundValues ( ) const

Since: 6.0

Returns a list of bound values.

The order of the list is in binding order, irrespective of whether named or positional binding is used.

The bound values can be examined in the following way:

    const QVariantList list = query.boundValues();
    for (qsizetype i = 0; i < list.size(); ++i)
        qDebug() << i << ":" << list.at(i).toString();

See also: boundValue(), bindValue(), addBindValue(), boundValueNames()

Definition at line 1176 of file qsqlquery.cpp.

◆ clear()

void QSqlQuery::clear ( )

Clears the result set and releases any resources held by the query.

Sets the query state to inactive. You should rarely if ever need to call this function.

Definition at line 949 of file qsqlquery.cpp.

◆ driver()

const QSqlDriver * QSqlQuery::driver ( ) const

Returns the database driver associated with the query.

Definition at line 496 of file qsqlquery.cpp.

◆ exec() [1/2]

bool QSqlQuery::exec ( )

Executes a previously prepared SQL query.

Returns true if the query executed successfully; otherwise returns false.

Note that the last error for this query is reset when exec() is called.

See also: prepare(), bindValue(), addBindValue(), boundValue(), boundValues()

Definition at line 1020 of file qsqlquery.cpp.

◆ exec() [2/2]

bool QSqlQuery::exec ( const QString & query )

Executes the SQL in query.

Returns true and sets the query state to \l{isActive()}{active} if the query was successful; otherwise returns false. 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 (for example, using next()).

Note that the last error for this query is reset when exec() is called.

For SQLite, the query string can contain only one statement at a time. If more than one statement is given, the function returns false.

Example:

    QSqlQuery query;
    query.exec("INSERT INTO employee (id, name, salary) "
               "VALUES (1001, 'Thad Beaumont', 65000)");

See also: isActive(), isValid(), next(), previous(), first(), last(), seek()

Definition at line 377 of file qsqlquery.cpp.

◆ execBatch()

bool QSqlQuery::execBatch ( BatchExecutionMode mode = ValuesAsRows )

Executes a previously prepared SQL query in a batch.

All the bound parameters have to be lists of variants. If the database doesn't support batch executions, the driver will simulate it using conventional exec() calls.

Returns true if the query is executed successfully; otherwise returns false.

Example:

QSqlQuery q;
q.prepare("insert into myTable values (?, ?)");
 
QVariantList ints;
ints << 1 << 2 << 3 << 4;
q.addBindValue(ints);
 
QVariantList names;
names << "Harald" << "Boris" << "Trond" << QVariant(QMetaType::fromType<QString>());
q.addBindValue(names);
 
if (!q.execBatch())
    qDebug() << q.lastError();

The example above inserts four new rows into myTable:

Harald
Boris
Trond
NULL

To bind NULL values, a null QVariant of the relevant type has to be added to the bound QVariantList; for example, {QVariant(QMetaType::fromType<QString>())} should be used if you are using strings.

Note: Every bound QVariantList must contain the same amount of variants.; The type of the QVariants in a list must not change. For example, you cannot mix integer and string variants within a QVariantList.

The mode parameter indicates how the bound QVariantList will be interpreted. If mode is ValuesAsRows, every variant within the QVariantList will be interpreted as a value for a new row. ValuesAsColumns is a special case for the Oracle driver. In this mode, every entry within a QVariantList will be interpreted as array-value for an IN or OUT value within a stored procedure. Note that this will only work if the IN or OUT value is a table-type consisting of only one column of a basic type, for example {TYPE myType IS TABLE OF VARCHAR(64) INDEX BY BINARY_INTEGER;}

See also: prepare(), bindValue(), addBindValue()

Definition at line 1087 of file qsqlquery.cpp.

◆ executedQuery()

QString QSqlQuery::executedQuery ( ) const

Returns the last query that was successfully executed.

In most cases this function returns the same string as lastQuery(). If a prepared query with placeholders is executed on a DBMS that does not support it, the preparation of this query is emulated. The placeholders in the original query are replaced with their bound values to form a new query. This function returns the modified query. It is mostly useful for debugging purposes.

See also: lastQuery()

Definition at line 1224 of file qsqlquery.cpp.

◆ finish()

void QSqlQuery::finish ( )

Instruct the database driver that no more data will be fetched from this query until it is re-executed.

There is normally no need to call this function, but it may be helpful in order to free resources such as locks or cursors if you intend to re-use the query at a later time.

Sets the query to inactive. Bound values retain their values.

See also: prepare(), exec(), isActive()

Definition at line 1335 of file qsqlquery.cpp.

◆ first()

bool QSqlQuery::first ( )

Retrieves the first record in the result, if available, and positions the query on the retrieved record.

Note that the result must be in the \l{isActive()}{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.

See also: next(), previous(), last(), seek(), at(), isActive(), isValid()

Definition at line 742 of file qsqlquery.cpp.

◆ isActive()

bool QSqlQuery::isActive ( ) const

Returns true if the query is {active}.

An active QSqlQuery is one that has been \l{QSqlQuery::exec()} {exec()'d} successfully but not yet finished with. When you are finished with an active query, you can make the query inactive by calling finish() or clear(), or you can delete the QSqlQuery instance.

Note: Of particular interest is an active query that is a {SELECT} statement. For some databases that support transactions, an active query that is a {SELECT} statement can cause a \l{QSqlDatabase::} {commit()} or a \l{QSqlDatabase::} {rollback()} to fail, so before committing or rolling back, you should make your active {SELECT} statement query inactive using one of the ways listed above.

See also: isSelect()

Definition at line 846 of file qsqlquery.cpp.

◆ isForwardOnly()

bool QSqlQuery::isForwardOnly ( ) const

Returns \l forwardOnly.

See also: forwardOnly, next(), seek()

Definition at line 866 of file qsqlquery.cpp.

◆ isNull() [1/2]

bool QSqlQuery::isNull ( int field ) const

Returns true if the query is not \l{isActive()}{active}, the query is not positioned on a valid record, there is no such field, or the field is null; otherwise 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(), value()

Definition at line 325 of file qsqlquery.cpp.

◆ isNull() [2/2]

bool QSqlQuery::isNull ( QAnyStringView name ) const

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.Returns true if there is no field with this name; otherwise returns isNull(int index) for the corresponding field index.

This overload is less efficient than \l{QSqlQuery::}{isNull()}

Note: In Qt versions prior to 6.8, this function took QString, not QAnyStringView.

Definition at line 343 of file qsqlquery.cpp.

◆ isPositionalBindingEnabled()

bool QSqlQuery::isPositionalBindingEnabled ( ) const

Returns \l positionalBindingEnabled.

Since: 6.7

See also: positionalBindingEnabled

Definition at line 1318 of file qsqlquery.cpp.

◆ isSelect()

bool QSqlQuery::isSelect ( ) const

Returns true if the current query is a SELECT statement; otherwise returns false.

Definition at line 856 of file qsqlquery.cpp.

◆ isValid()

bool QSqlQuery::isValid ( ) const

Returns true if the query is currently positioned on a valid record; otherwise returns false.

Definition at line 824 of file qsqlquery.cpp.

◆ last()

bool QSqlQuery::last ( )

Retrieves the last record in the result, if available, and positions the query on the retrieved record.

Note that the result must be in the \l{isActive()}{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.

See also: next(), previous(), first(), seek(), at(), isActive(), isValid()

Definition at line 765 of file qsqlquery.cpp.

◆ lastError()

QSqlError QSqlQuery::lastError ( ) const

Returns error information about the last error (if any) that occurred with this query.

See also: QSqlError, QSqlDatabase::lastError()

Definition at line 814 of file qsqlquery.cpp.

◆ lastInsertId()

QVariant QSqlQuery::lastInsertId ( ) const

Returns the object ID of the most recent inserted row if the database supports it.

An invalid QVariant will be returned if the query did not insert any value or if the database does not report the id back. If more than one row was touched by the insert, the behavior is undefined.

For MySQL databases the row's auto-increment field will be returned.

Note: For this function to work in PSQL, the table must contain OIDs, which may not have been created by default. Check the default_with_oids configuration variable to be sure.

See also: QSqlDriver::hasFeature()

Definition at line 1244 of file qsqlquery.cpp.

◆ lastQuery()

QString QSqlQuery::lastQuery ( ) const

Returns the text of the current query being used, or an empty string if there is no current query text.

See also: executedQuery()

Definition at line 487 of file qsqlquery.cpp.

◆ next()

bool QSqlQuery::next ( )

Retrieves the next record in the result, if available, and positions the query on the retrieved record.

Note that the result must be in the \l{isActive()}{active} state and isSelect() must return true before calling this function or it will do nothing and return false.

The following rules apply:

\list

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.

\endlist

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: previous(), first(), last(), seek(), at(), isActive(), isValid()

Definition at line 661 of file qsqlquery.cpp.

◆ nextResult()

bool QSqlQuery::nextResult ( )

Discards the current result set and navigates to the next if available.

Some databases are capable of returning multiple result sets for stored procedures or SQL batches (a query strings that contains multiple statements). If multiple result sets are available after executing a query this function can be used to navigate to the next result set(s).

If a new result set is available this function will return true. The query will be repositioned on an invalid record in the new result set and must be navigated to a valid record before data values can be retrieved. If a new result set isn't available the function returns false and the query is set to inactive. In any case the old result set will be discarded.

When one of the statements is a non-select statement a count of affected rows may be available instead of a result set.

Note that some databases, i.e. Microsoft SQL Server, requires non-scrollable cursors when working with multiple result sets. Some databases may execute all statements at once while others may delay the execution until the result set is actually accessed, and some databases may have restrictions on which statements are allowed to be used in a SQL batch.

See also: QSqlDriver::hasFeature(), forwardOnly, next(), isSelect(), numRowsAffected(), isActive(), lastError()

Definition at line 1374 of file qsqlquery.cpp.

◆ numericalPrecisionPolicy()

QSql::NumericalPrecisionPolicy QSqlQuery::numericalPrecisionPolicy ( ) const

Returns the \l numericalPrecisionPolicy.

Definition at line 1284 of file qsqlquery.cpp.

◆ numRowsAffected()

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, the value is undefined; use size() instead. If the query is not \l{isActive()}{active}, -1 is returned.

See also: size(), QSqlDriver::hasFeature()

Definition at line 800 of file qsqlquery.cpp.

◆ operator=()

QSqlQuery & QSqlQuery::operator= ( const QSqlQuery & other )

delete

Since: 6.2 Move-assigns other to this object.

◆ prepare()

bool QSqlQuery::prepare ( const QString & query )

Prepares the SQL query query for execution.

Returns true if the query is prepared successfully; otherwise returns false.

The query may contain placeholders for binding values. Both Oracle style colon-name (e.g., {:surname}), and ODBC style ({?}) placeholders are supported; but they cannot be mixed in the same query. See the \l{QSqlQuery examples}{Detailed Description} for examples.

Portability notes: Some databases choose to delay preparing a query until it is executed the first time. In this case, preparing a syntactically wrong query succeeds, but every consecutive exec() will fail. When the database does not support named placeholders directly, the placeholder can only contain characters in the range [a-zA-Z0-9_].

For SQLite, the query string can contain only one statement at a time. If more than one statement is given, the function returns false.

Example:

    QSqlQuery query;
    query.prepare("INSERT INTO person (id, forename, surname) "
                  "VALUES (:id, :forename, :surname)");
    query.bindValue(":id", 1001);
    query.bindValue(":forename", "Bart");
    query.bindValue(":surname", "Simpson");
    query.exec();

See also: exec(), bindValue(), addBindValue()

Definition at line 980 of file qsqlquery.cpp.

◆ previous()

bool QSqlQuery::previous ( )

Retrieves the previous record in the result, if available, and positions the query on the retrieved record.

Note that the result must be in the \l{isActive()}{active} state and isSelect() must return true before calling this function or it will do nothing and return false.

The following rules apply:

\list

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.

\endlist

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: next(), first(), last(), seek(), at(), isActive(), isValid()

Definition at line 709 of file qsqlquery.cpp.

◆ record()

QSqlRecord QSqlQuery::record ( ) const

Returns a QSqlRecord containing the field information for the current query.

If the query points to a valid row (isValid() returns true), the record is populated with the row's values. An empty record is returned when there is no active query (isActive() returns false).

To retrieve values from a query, value() should be used since its index-based lookup is faster.

In the following example, a {SELECT * FROM} query is executed. Since the order of the columns is not defined, QSqlRecord::indexOf() is used to obtain the index of a column.

QSqlQuery q("select * from employees");
QSqlRecord rec = q.record();
 
qDebug() << "Number of columns: " << rec.count();
 
int nameCol = rec.indexOf("name"); // index of the field "name"
while (q.next())
    qDebug() << q.value(nameCol).toString(); // output all names

See also: value()

Definition at line 933 of file qsqlquery.cpp.

◆ result()

const QSqlResult * QSqlQuery::result ( ) const

Returns the result associated with the query.

Definition at line 505 of file qsqlquery.cpp.

◆ seek()

bool QSqlQuery::seek	(	int	index,
		bool	relative = false )

Retrieves the record at position index, if available, and positions the query on the retrieved record.

The first record is at position 0. Note that the query must be in an \l{isActive()} {active} state and isSelect() must return true before calling this function.

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

\list

If index 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 index. If the record at position index 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.

\endlist

If relative is true, the following rules apply:

\list

If the result is currently positioned before the first record and: \list
index is negative or zero, there is no change, and false is returned.
index is positive, an attempt is made to position the result at absolute position index - 1, following the sames rule for non relative seek, above. \endlist

If the result is currently positioned after the last record and: \list
index is positive or zero, there is no change, and false is returned.
index is negative, an attempt is made to position the result at index + 1 relative position from last record, following the rule below. \endlist

If the result is currently located somewhere in the middle, and the relative offset index 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 index records ahead of the current record (or index records behind the current record if index is negative). If the record at offset index could not be retrieved, the result is positioned after the last record if index >= 0, (or before the first record if index is negative), and false is returned. If the record is successfully retrieved, true is returned.

\endlist

See also: next(), previous(), first(), last(), at(), isActive(), isValid()

Definition at line 569 of file qsqlquery.cpp.

◆ setForwardOnly()

void QSqlQuery::setForwardOnly ( bool forward )

Sets \l forwardOnly to forward.

See also: forwardOnly, next(), seek()

Definition at line 910 of file qsqlquery.cpp.

◆ setNumericalPrecisionPolicy()

void QSqlQuery::setNumericalPrecisionPolicy ( QSql::NumericalPrecisionPolicy precisionPolicy )

Sets \l numericalPrecisionPolicy to precisionPolicy.

Definition at line 1276 of file qsqlquery.cpp.

◆ setPositionalBindingEnabled()

void QSqlQuery::setPositionalBindingEnabled ( bool enable )

Sets \l positionalBindingEnabled to enable.

Since: 6.7

See also: positionalBindingEnabled

Definition at line 1308 of file qsqlquery.cpp.

◆ size()

int QSqlQuery::size ( ) const

Returns the size of the result (number of rows returned), or -1 if the size cannot be determined or if 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(), QSqlDriver::hasFeature()

Definition at line 784 of file qsqlquery.cpp.

◆ swap()

void QSqlQuery::swap ( QSqlQuery & other )

inlinenoexcept

Since: 6.2 \memberswap{query}

Definition at line 52 of file qsqlquery.h.

◆ value() [1/2]

QVariant QSqlQuery::value ( int index ) const

Returns the value of field index in the current record.

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 index does not exist, if the query is inactive, or if the query is positioned on an invalid record.

See also: previous(), next(), first(), last(), seek(), isActive(), isValid()

Definition at line 438 of file qsqlquery.cpp.

◆ value() [2/2]

QVariant QSqlQuery::value ( QAnyStringView name ) const

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.Returns the value of the field called name in the current record.

If field name does not exist an invalid variant is returned.

This overload is less efficient than \l{QSqlQuery::}{value()}

Note: In Qt versions prior to 6.8, this function took QString, not QAnyStringView.

Definition at line 457 of file qsqlquery.cpp.

Property Documentation

◆ forwardOnly

bool QSqlQuery::forwardOnly

readwrite

Since: 6.8

This property holds the forward only mode. If forward is true, only next() and seek() with positive values, are allowed for navigating the results.

Forward only mode can be (depending on the driver) more memory efficient since results do not need to be cached. It will also improve performance on some databases. For this to be true, you must call setForwardOnly() before the query is prepared or executed. Note that the constructor that takes a query and a database may execute the query.

Forward only mode is off by default.

Setting forward only to false is a suggestion to the database engine, which has the final say on whether a result set is forward only or scrollable. isForwardOnly() will always return the correct status of the result set.

Note: Calling setForwardOnly after execution of the query will result in unexpected results at best, and crashes at worst.; To make sure the forward-only query completed successfully, the application should check lastError() for an error not only after executing the query, but also after navigating the query results.

Warning: PostgreSQL: While navigating the query results in forward-only mode, do not execute any other SQL command on the same database connection. This will cause the query results to be lost.

See also: next(), seek()

Definition at line 26 of file qsqlquery.h.

◆ numericalPrecisionPolicy

QSql::NumericalPrecisionPolicy QSqlQuery::numericalPrecisionPolicy

readwrite

Since: 6.8

Instruct the database driver to return numerical values with a precision specified by precisionPolicy.

The Oracle driver, for example, can retrieve numerical values as strings to prevent the loss of precision. If high precision doesn't matter, use this method to increase execution speed by bypassing string conversions.

Note: Drivers that don't support fetching numerical values with low precision will ignore the precision policy. You can use QSqlDriver::hasFeature() to find out whether a driver supports this feature.

Note: Setting the precision policy doesn't affect the currently active query. Call \l{exec()}{exec(QString)} or prepare() in order to activate the policy.

See also: QSql::NumericalPrecisionPolicy, QSqlDriver::numericalPrecisionPolicy, QSqlDatabase::numericalPrecisionPolicy

Definition at line 28 of file qsqlquery.h.

◆ positionalBindingEnabled

bool QSqlQuery::positionalBindingEnabled

readwrite

Since: 6.8 This property enables or disables the positional \l {Approaches to Binding Values}{binding} for this query, depending on enable (default is true). Disabling positional bindings is useful if the query itself contains a '?' which must not be handled as a positional binding parameter but, for example, as a JSON operator for a PostgreSQL database.

This property will have no effect when the database has native support for positional bindings with question marks (see also \l{QSqlDriver::PositionalPlaceholders}).

Definition at line 27 of file qsqlquery.h.

The documentation for this class was generated from the following files:

qtbase/src/sql/kernel/qsqlquery.h (f744cef06cf3a56591782f487c545b55b2a673fb)
qtbase/src/sql/kernel/qsqlquery.cpp (cf93005bb11272ab812c3ddbf17308ecf7322ad4)

Public Types

Public Member Functions

Properties

Detailed Description

Member Enumeration Documentation

◆ BatchExecutionMode

Constructor & Destructor Documentation

◆ QSqlQuery() [1/5]

◆ QSqlQuery() [2/5]

◆ QSqlQuery() [3/5]

◆ QSqlQuery() [4/5]

◆ QSqlQuery() [5/5]

◆ ~QSqlQuery()

Member Function Documentation

◆ addBindValue()

◆ at()

◆ bindValue() [1/2]

◆ bindValue() [2/2]

◆ boundValue() [1/2]

◆ boundValue() [2/2]

◆ boundValueName()

◆ boundValueNames()

◆ boundValues()

◆ clear()

◆ driver()

◆ exec() [1/2]

◆ exec() [2/2]

◆ execBatch()

◆ executedQuery()

◆ finish()

◆ first()

◆ isActive()

◆ isForwardOnly()

◆ isNull() [1/2]

◆ isNull() [2/2]

◆ isPositionalBindingEnabled()

◆ isSelect()

◆ isValid()

◆ last()

◆ lastError()

◆ lastInsertId()

◆ lastQuery()

◆ next()

◆ nextResult()

◆ numericalPrecisionPolicy()

◆ numRowsAffected()

◆ operator=()

◆ prepare()

◆ previous()

◆ record()

◆ result()

◆ seek()

◆ setForwardOnly()

◆ setNumericalPrecisionPolicy()

◆ setPositionalBindingEnabled()

◆ size()

◆ swap()

◆ value() [1/2]

◆ value() [2/2]

Property Documentation

◆ forwardOnly

◆ numericalPrecisionPolicy

◆ positionalBindingEnabled