检查数据库文件中是否存在 ID 时出错

Question

我正在尝试检查某个 ID 是否已存在于数据库中。如果没有，我希望用户将 id 更改为其他内容。

这一切都在 textobx 的TextChanged 函数中完成。

问题是我遇到了一个错误，由于查询看起来不错，我不确定为什么会看到这个：The SELECT statement includes a reserved word or an argument name that is misspelled or missing, or the punctuation is incorrect.

检查方法：

private bool DoesIDExist(int dataID, string filePath)
{
    HashPhrase hash = new HashPhrase();
    DataTable temp = new DataTable();

    string hashShortPass = hash.ShortHash(pass);
    bool result = false;

    // Creating a connection string. Using placeholders make code
    // easier to understand.
    string connectionString =
        @"Provider=Microsoft.ACE.OLEDB.12.0; Data Source={0};
          Persist Security Info=False; Jet OLEDB:Database Password={1};";

    string sql = string.Format
        ("SELECT FROM PersonalData WHERE [DataID] = {0}", dataID);

    using (OleDbConnection connection = new OleDbConnection())
    {
        // Creating command object.
        // Using a string formatting let me to insert data into
        // place holders I have used earlier.
        connection.ConnectionString =
            string.Format(connectionString, filePath, hashShortPass);

        using (OleDbCommand command = new OleDbCommand(sql, connection))
        {
            // Creating command object.
            // Using a string formatting let me to insert data into
            // place holders I have used earlier.
            connection.ConnectionString =
                string.Format(connectionString, filePath, hashShortPass);

            try
            {
                // Open database connection.
                connection.Open();

                using (OleDbDataReader read = command.ExecuteReader())
                {
                    // Checking if there is any data in the file.
                    if (read.HasRows)
                    {
                        // Reading information from the file.
                        while (read.Read())
                        {
                            if (read.GetInt32(0) == dataID)
                                return true;
                        }
                    }
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show("Error: " + ex.Message);
            }
        }
    }

    return result;
}

Answer 1

我认为您的选择缺少一些您想要提取的列？？

string sql = string.Format
    ("SELECT FROM PersonalData WHERE [DataID] = {0}", dataID);

不应该是这样的：

string sql = string.Format
    ("SELECT * FROM PersonalData WHERE [DataID] = {0}", dataID);

Answer 2

您缺少要选择的内容

string sql = string.Format
    ("SELECT FROM PersonalData WHERE [DataID] = {0}", dataID);

改成类似

string sql = string.Format
    ("SELECT * FROM PersonalData WHERE [DataID] = {0}", dataID);

而且：您可以像构建查询一样使用 SQL 注入。

Answer 3

您需要在SELECT 子句中指定一些内容。我猜：

SELECT DataID FROM PersonalData WHERE ...

Answer 4

问题在于这行代码：

string sql = string.Format
        ("SELECT FROM PersonalData WHERE [DataID] = {0}", dataID);

您需要指定要选择的内容。示例：SELECT *、SELECT [MyColumn]、SELECT TOP 1 * 等。根据您的要求，您正在寻找类似的东西：

string sql = string.Format
 ("SELECT COUNT(*) AS UserCount FROM PersonalData WHERE [DataID] = {0}", dataID);

其他信息：

如果在网络上使用此方法，例如从查询字符串中提取一个 ID，那么您将面临 SQL 注入攻击。稍微修改您的代码将解决问题：

string sql = "SELECT FROM PersonalData WHERE [DataID] = @DataID";

using (OleDbCommand command = new OleDbCommand(sql, connection))
        {
            command.Parameters.AddWithValue("@DataID", dataID);
        }