parameter count mismatch in parameterized query

问题

I am using quite a lot of parameterized queries in my code for performance reasons. In short, some of them work, some don't.

I initialize the query during construction of my database wrapper like this:

QString querystring = QString("SELECT somevalue FROM sometable "
                      "WHERE one_feature = :one_feature AND other_feature = :other_feature ");
myquery = QSqlQuery(db);
myquery.setForwardOnly(true);
myquery.prepare(querystring);

myquery is a QSqlQuery member variable of my database wrapper. Later on, in the function that wants to use this query, I do something like

int db_wrapper::fetch_some_value (int arg1, int arg2) {
    myquery.clear();
    myquery.bindValue(":one_feature", arg1);
    myquery.bindValue(":other_feature", arg2);

    qDebug() << "Bound values: " << myquery.boundValues();

    bool OK = myquery.exec();
    if (!OK) {
        int number = myquery.lastError().number();
        qDebug() << "db error " << number;
        qDebug() << "db error " << myquery.lastError().text();

#ifdef USE_EXCEPTIONS
        throw "Could not fetch some_value!";
#endif
    }

    // process data...
}

I always get the same error message/output:

Bound values:  QMap((":one_feature", QVariant(int, 1) ) ( ":other_feature" ,  QVariant(int, 1) ) )  
db error  -1 
db error  " Parameter count mismatch" 
terminate called after throwing an instance of 'char const*'

The exception is not surprising, but the parameter count mismatch is. The call to boundValues actually shows the right values and all, still I get this error message. I have similar queries that work just fine.

I tried substituting positional bind values, renamed the placeholders, used ? and positional bind values, all to no avail. Does anyone have an idea what the problem might be?

I use Qt 4.7.3 and SQLite 3.7.4-2

回答1:

Usually this error means that the SELECT/UPDATE query itself is incorrect. You did not give the schema of the database so it's not possible to pinpoint which one. So one or more of somevalue, sometable, one_feature, or second_feature is not in the database/table.

来源：https://stackoverflow.com/questions/7525996/parameter-count-mismatch-in-parameterized-query

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c++

sqlite

qtsql