Question

我需要一些帮助。我有这个代码（下面），将数据添加到MySQL表，然后返回相同的表。代码运行正常，当我运行它时，它将列添加到MySQL表但它停止，错误：

SQL error. Error message:

字面上一片空白。如果我在SELECT中使用INCLUDE语句而不是executeQuery()语句，它运行没有问题且没有错误消息，只显示我的表（或部分表）。我错过了什么？

我正在使用Visual Studios 2015和MySQL Server。

最终目标是使用C ++将API与SQL表连接，以根据特定的时间跨度记录数据。这是最初的步骤之一，只是为了确保我可以正确地将MySQL与C ++链接起来。

很抱歉，如果这篇文章写得不好，第一次来这里，绝对不是一位经验丰富的程序员...另外，我调查了其他主题，但由于这是如此具体，我找不到它们有用。

// Standard C++ includes
#include <iostream>
#include <cstdlib>
#include <string>
using namespace std;

// Include the Connector/C++ headers
#include "cppconn/driver.h"
#include "cppconn/exception.h"
#include "cppconn/resultset.h"
#include "cppconn/statement.h"

// Link to the Connector/C++ library
#pragma comment(lib, "mysqlcppconn.lib")

// Specify our connection target and credentials
const string server = "127.0.0.1:3306";
const string username = "root";
const string password = "root";
const string database = "dbex"; 
const string table = "tbex";

int main()
{
    sql::Driver     *driver; // Create a pointer to a MySQL driver object
    sql::Connection *dbConn; // Create a pointer to a database connection object
    sql::Statement  *stmt;   // Create a pointer to a Statement object to hold our SQL commands
    sql::ResultSet  *res;    // Create a pointer to a ResultSet object to hold the results of any queries we run

                             // Try to get a driver to use to connect to our DBMS
    try
    {
        driver = get_driver_instance();
    }
    catch (sql::SQLException e)
    {
        cout << "Could not get a database driver. Error message: " << e.what() << endl;
        system("pause");
        exit(1);
    }

    // Try to connect to the DBMS server
    try
    {
        dbConn = driver->connect(server, username, password);
        dbConn->setSchema(database);
    }
    catch (sql::SQLException e)
    {
        cout << "Could not connect to database. Error message: " << e.what() << endl;
        system("pause");
        exit(1);
    }
    stmt = dbConn->createStatement();

    // Try to query the database
    try
    {
        //stmt->execute("USE " + database);              // Select which database to use. Notice that we use "execute" to perform a command.
        res = stmt->executeQuery("INSERT INTO "+ table +"(Brand, Model, Power, `Last Used`,`# Times Used`) VALUES('Ferrari','Modena','500','Never',0)"); 
        res = stmt->executeQuery("SELECT * FROM cars"); // Perform a query and get the results. Notice that we use "executeQuery" to get results back

    }
    catch (sql::SQLException e)
    {
        cout << "SQL error. Error message: " << e.what() << endl;
        system("pause");
        exit(1);
    }

// While there are still results (i.e. rows/records) in our result set...
    while (res->next())
    {
        cout << res->getString(1) << endl;
    }

    delete res;
    delete stmt;
    delete dbConn;

    system("pause");
    return 0;
}

提前致谢

Answer 1

检查一下：

排队：

res = stmt->executeQuery("INSERT INTO "+ table +"(Brand, Model, Power, `Last Used`,`# Times Used`) VALUES('Ferrari','Modena','500','Never',0)");

您正在进行错误的字符串连接，+（加号）运算符不会以这种方式工作，代码不会连接字符串，而是添加指针。

只需简单地替换这种方式再试一次：

#define TABLE "tbex"// put this in top of cpp file
......
res = stmt->executeQuery("INSERT INTO " TABLE "(Brand, Model, Power, `Last Used`
,`# Times Used`) VALUES('Ferrari','Modena','500','Never',0)");

Answer 2

INSERT不是查询。尝试使用executeUpdate（）而不是executeQuery（）。

替换此行

res = stmt->executeQuery("INSERT INTO "+ table +"(Brand, Model, Power, `Last Used`,`# Times Used`) VALUES('Ferrari','Modena','500','Never',0)");

使用以下行（您可能需要一个额外的.h文件）：

sql::PreparedStatement *pstmt;

pstmt = con->prepareStatement("INSERT INTO "+ table +"(Brand, Model, Power, `Last Used`,`# Times Used`) VALUES('Ferrari','Modena','500','Never',0)");
res = pstmt->executeUpdate();
delete pstmt;

查看官方MySQL示例here以获取该概念的示例。

您也可以尝试使用execute（），如this Stackoverflow问题所示。函数execute（）用于通用SQL命令，但在返回值中可能不像更多指定函数那样冗长（它返回一个布尔值）。

C ++ executeQuery（）错误显示表中的MySQL数据

2 个答案: