Problems with connection and verification in Access c# databases

[Nlech3]

For a student project I need to create an application with an Access database, but I don't know anything about databases. Can anyone explain what the problem is?

private void button1_Click(object sender, EventArgs e)
{

DataPerson.Full_name = textBox1.Text;
DataPerson.Address = textBox2.Text;
DataPerson.Contract_number = textBox3.Text;
DataPerson.Telephone = textBox4.Text;

string connectionString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:\\IT\\WindowsFormsApp1\\WindowsFormsApp1\\Microsoft Access Database.accdb";

using (OleDbConnection connection = new OleDbConnection(connectionString))
{
    try
    {
        connection.Open();

        string query = "SELECT 1-3 FROM Table1 ФИО = @ФИО AND Адрес = @Адрес AND Номер_Договора = @Номер_Договора AND Телефон = @Телефон";

        OleDbCommand command = new OleDbCommand(query, connection);
        command.Parameters.AddWithValue("@ФИО", DataPerson.Full_name);
        command.Parameters.AddWithValue("@Адрес", DataPerson.Address);
        command.Parameters.AddWithValue("@Номер_Договора", DataPerson.Contract_number);
        command.Parameters.AddWithValue("@Телефон", DataPerson.Telephone);
        int count = Convert.ToInt32(command.ExecuteScalar());

        if (count > 3)
        {
            MessageBox.Show("Успешная авторизация!");
        }
        else 
        {
            MessageBox.Show("Неудачная авторизация или отсутствие аккаунта!");
        }
    }
    catch (Exception ex)
    {
        MessageBox.Show("Error: " + ex.ToString());
    }
    finally
    {
        connection.Close();
    }
}

}

[MaceWindu]

You have syntax error in your query.

If you format your query it should be obvious that you miss WHERE keyword before query filter:

SELECT 1-3
    FROM Table1
    WHERE -- missing part
    ФИО = @ФИО AND Адрес = @Адрес AND Номер_Договора = @Номер_Договора AND Телефон = @Телефон

Check Access reference here https://learn.microsoft.com/en-us/office/client-developer/access/desktop-database-reference/select-statement-microsoft-access-sql

[MaceWindu]

BTW,

1. your select expression 1-3 is strange. It's same as -2 and will never be > 3
2. query will return 0 records if filter returns false. Better to use COUNT aggregate instead: SELECT COUNT(*) and check resulting number being equal to 1 (record)