Question

好的，我的代码中有2个方法：一个用于创建数据库，另一个用于插入记录。他们在这里：

void DatabaseManager::insert_entry_into_database() {
ostringstream ss;
int choice;

do {
    cout << "Press 1 to add a teacher or 2 for student";
    cin >> choice;
} while (choice != 1 && choice != 2);       

if (choice == 1) {
    Teacher t;
    ss << "INSERT INTO Teachers ('" << t.get_firstName() << "', '" << t.get_lastName() << "', " << t.get_NID() 
        << ", " << t.get_avg_horarium() << ");";
}

const string tmp = ss.str();
const char *query = tmp.c_str();

cout << query;

sqlite3_open("Database.sqlite", &database);
if (sqlite3_prepare_v2(database, query, -1, &statement, 0) == SQLITE_OK) {
    cout << "A new record has been added to the database!" << endl;
}
else {
    cout << "Error adding new record!";
}   
sqlite3_finalize(statement);
sqlite3_close(database); 
}

void DatabaseManager::create_database() {
sqlite3_open("Database.sqlite", &database);

char * query = "CREATE TABLE Students (firstName STRING, lastName STRING, NID BIGINT, grade DOUBLE);";

if (sqlite3_prepare_v2(database, query, -1, &statement, 0) == SQLITE_OK) {
    cout << "Empty database with students created!" << endl;
}

query = "CREATE TABLE Teachers (firstName STRING, lastName STRING, NID BIGINT, avg_horarium INT);";

if (sqlite3_prepare_v2(database, query, -1, &statement, 0) == SQLITE_OK) {
    cout << "Empty database with teachers created!" << endl;
}

sqlite3_finalize(statement);
sqlite3_close(database);

}

我在主函数中测试它们：

int _tmain(int argc, _TCHAR* argv[])
{
DatabaseManager m;
m.create_database();
m.insert_entry_into_database();
return 0;
}

create table查询似乎是成功的，并且控制台上显示确认消息，但insert查询被视为无效。我添加了一个cout＆lt;＆lt;查询调用以确保它是正确的并且百分之百有效。这有什么问题？

选择方法

vector<vector<string>> DatabaseManager::select_entry() {
vector<vector<string>> results;
sqlite3_open("Database.sqlite", &database);

char* query = "SELECT firstName FROM Teachers WHERE firstName = 'Ivan';";
cout << query;

if (sqlite3_prepare_v2(database, query, -1, &statement, 0) == SQLITE_OK) {
    int cols = sqlite3_column_count(statement);
    int result = 0;

    while (true) {
        result = sqlite3_step(statement);

        if (result == SQLITE_ROW) {
            cout << "test"; 
            vector<string> values;
            for (int i=0; i<cols; i++) {
                cout << (char*)sqlite3_column_text(statement, i);
                values.push_back((char*)sqlite3_column_text(statement, i));
            }
            results.push_back(values);
        }
        else break;
    }

    sqlite3_finalize(statement);
    string error = sqlite3_errmsg(database);
    if(error != "not an error") cout << query << " " << error << endl;

    return results;
}

}

Answer 1

valid syntax for an INSERT statement是

INSERT INTO MyTable(Col1, Col2, ...) VALUES (value1, value2, ...)

或

INSERT INTO MyTable VALUES (value1, value2, ...)

您已省略VALUES，因此SQLite认为括号内的内容是列名列表。

数据库文件由sqlite3_open自动创建。

您需要致电sqlite3_step来实际执行命令。

在C ++中使用SQLite执行查询时出错

1 个答案: