QSqlQuery

QSqlQuery is a class in the Qt framework that provides a way to execute SQL statements and interact with databases. It allows developers to perform operations such as querying data, inserting, updating, and deleting records. QSqlQuery is part of the Qt SQL module, which offers a database-independent interface to various SQL databases.

To use QSqlQuery, you first need to establish a database connection using QSqlDatabase. Once a connection is active, you can create a QSqlQuery object, passing the QSqlDatabase object to its constructor or by calling setDatabase(). The primary method for executing SQL commands is exec(), which takes a SQL query string as an argument.

After executing a SELECT query, QSqlQuery provides methods to navigate through the result set. QSqlQuery::next() moves to the next row, returning true if successful. QSqlQuery::first() and QSqlQuery::last() move to the beginning and end of the result set, respectively. The values within a row can be retrieved using methods like QSqlQuery::value(), which takes a column index or name as input. QSqlQuery::isValid() checks if the current position is valid, and QSqlQuery::numRows() returns the total number of rows in the result set.

For data modification queries (INSERT, UPDATE, DELETE), QSqlQuery::exec() returns true if the operation was successful. Error handling is crucial, and QSqlQuery provides methods like QSqlQuery::lastError() to retrieve details about any issues that occurred during query execution. QSqlQuery also supports prepared statements and bound values, which help prevent SQL injection vulnerabilities and improve performance.