mysql结果集是空的吗？

Question

编辑

跟进问题：mysql resultset is always null

--

resultset似乎是空的，而且我确信表是存在的，没有抛出SQLException。它应该打印计数，但它没有。

CDatabase报头

class CDatabase
{
    bool verify(string, string);
public:
    sql::Connection *con;
    CDatabase();
    ~CDatabase();
};

CDatabase::CDatabase

con = driver->connect("", "", "");
con->setSchema("");

CDatabase::verify

bool CDatabase::verify(string channel, string hyper_key)
{
    if (!con) return false;
    try
    {
        sql::Statement *stmt;
        sql::ResultSet *res;
        stmt = con->createStatement();
        stmt->execute("SELECT COUNT(*) FROM dark_souls2_widgets");
        res = stmt->getResultSet();
        cout << res->rowsCount();
        delete stmt;
        delete res;
    }
    catch (sql::SQLException &e) {
        cout << "# ERR: SQLException in " << __FILE__;
        cout << "(" << __FUNCTION__ << ") on line »" << __LINE__ << endl;
        cout << "# ERR: " << e.what();
        cout << " (MySQL error code: " << e.getErrorCode();
        cout << ", SQLState: " << e.getSQLState() << " )" << endl;
        return false;
    }
    return false;
}

Answer 1

它不应该显示计数，它应该显示1，因为这个查询要么失败，要么结果只有一行。如果您想知道您的表dark_souls2_widgets中有多少行，那么您可以使用

res = stmt->getResultSet();

while (res->next()) {
  cout << res->getInt(1); // getInt(1) returns the first column
}

Answer 2

我已经有一段时间没有在c++上使用mysql了，但我想试一试.这是来自dev.mysql的一个例子

stmt = con->createStatement();
res = stmt->executeQuery("SELECT 'Hello World!' AS _message");
while (res->next()) {
    cout << "\t... MySQL replies: ";
    /* Access column data by alias or column name */
    cout << res->getString("_message") << endl;
    cout << "\t... MySQL says it again: ";
    /* Access column fata by numeric offset, 1 is the first column */
    cout << res->getString(1) << endl;
}

首先，我注意到您使用的是execute()而不是executeQuery()。最重要的是，如果rowsCount()成功的话，它总是1行，因为查询只返回1行，这是查询的结果。试试这个..。

stmt->executeQuery("SELECT COUNT(*) FROM dark_souls2_widgets");
res = stmt->getResultSet();
while (res->next()) {
    cout << res->getInt(1);
}

或者即使这样也能工作，因为它将选择每一行并输出返回的行数。

stmt->executeQuery("SELECT * FROM dark_souls2_widgets");
cout << res->rowsCount();

编辑-试试这个

stmt = con->creteStatement()
res = stmt->executeQuery("SELECT COUNT(*) FROM dark_souls2_widgets");
while (res->next()) {
    cout << res->getInt(1);
}