Most efficient way to iterate through a QSqlQuery result set?

Question

I'm querying a remote MSSQL Server database using QODBC and I have a result set returned but it appears as though it sends a query to SQL Server for each record one by one. This is really slow for iterating a result set. Running the query from Qt, it takes roughly 15 seconds to complete. I ran the same query in SQL Server Management Studio and it takes 1 second to return results. Here's the code I'm using: ``` QString connectionTemplate = "DRIVER={SQL SERVER};SERVER=server;DATABASE=db;"; QSqlDatabase db = QSqlDatabase::addDatabase("QODBC3", "db"); db.setDatabaseName(connectionTemplate); db.setUserName("user"); db.setPassword("password"); if (db.open()) { qDebug() << "OK!"; QSqlQuery * query = new QSqlQuery(db); query->exec("SELECT [UserName]" " FROM [dbo].[Users]"); while(query->next()) { QString userName = query->value(0).toString(); qDebug() << userName; } db.close(); } else { qDebug() << db.lastError().text(); } ``` Is there any way to capture the entire result set into memory and…

Accepted Answer

I figured out how to improve the speed of iterating through the results. I had forgotten that I needed to first prepare the sql before executing and `setForwardOnly` must be set to true.

```
QSqlQuery * query = new QSqlQuery(db);
query->setForwardOnly(true);
query->exec("SELECT [UserName]"
            "  FROM [dbo].[Users]");
```

Most efficient way to iterate through a QSqlQuery result set?

Solution

Problem