Извлечь запись из базы данных, где значение времени равно null

Question

Я пытаюсь обновить строку в базе данных, где одно из значений даты/времени пуст.

Код, приведенный ниже, дает ошибку: - Параметр? _2 не имеет значения по умолчанию.

Кто-нибудь знает, как работать с нулевыми/пустыми значениями?

Приветствия

OleDbCommand com = new OleDbCommand("SELECT count(*) from DI WHERE [Task] = ? AND [Time_Off] = ?", Program.DB_CONNECTION); 
com.Parameters.Add(new OleDbParameter("", "DI")); 
com.Parameters.Add(new OleDbParameter("", null)); 
int count = (int)com.ExecuteScalar(); 

if (count > 0) 
{ 
    OleDbCommand com1 = new OleDbCommand("UPDATE DI SET [Time_OFF] = ? WHERE [Task] = ? AND [Time_Off] = ?", Program.DB_CONNECTION); 
    com1.Parameters.Add(new OleDbParameter("", DateTime.Now.TimeOfDay)); 
    com1.Parameters.Add(new OleDbParameter("", "DI")); 
    com1.Parameters.Add(new OleDbParameter("", null)); 
    com1.ExecuteNonQuery(); 
} 
else 
{ 
    DIPerson = DIlist[DIcomboBox.SelectedIndex]; 

    OleDbCommand com2 = new OleDbCommand("INSERT INTO DI ([Person], [Task], [Time_On]) VALUES (?, ?, ?)", Program.DB_CONNECTION); 
    com2.Parameters.Add(new OleDbParameter("", DIPerson.ID)); 
    com2.Parameters.Add(new OleDbParameter("", "DI")); 
    com2.Parameters.Add(new OleDbParameter("", DateTime.Now.TimeOfDay)); 

    com2.ExecuteNonQuery(); 
} 

Answer 1

OleDbCommand com = new OleDbCommand("SELECT count(*) from DI WHERE [Task] = ? AND [Time_Off] is null", Program.DB_CONNECTION); 
com.Parameters.Add(new OleDbParameter("", "DI")); 
int count = (int)com.ExecuteScalar(); 

if (count > 0) 
{ 
    OleDbCommand com1 = new OleDbCommand("UPDATE DI SET [Time_OFF] = ? WHERE [Task] = ? AND [Time_Off] is null", Program.DB_CONNECTION); 
    com1.Parameters.Add(new OleDbParameter("", DateTime.Now.TimeOfDay)); 
    com1.Parameters.Add(new OleDbParameter("", "DI")); 
    com1.ExecuteNonQuery(); 
} 
else 
{ 
    DIPerson = DIlist[DIcomboBox.SelectedIndex]; 

    OleDbCommand com2 = new OleDbCommand("INSERT INTO DI ([Person], [Task], [Time_On]) VALUES  (?, ?, ?)", Program.DB_CONNECTION); 
    com2.Parameters.Add(new OleDbParameter("", DIPerson.ID)); 
    com2.Parameters.Add(new OleDbParameter("", "DI")); 
    com2.Parameters.Add(new OleDbParameter("", DateTime.Now.TimeOfDay)); 

    com2.ExecuteNonQuery(); 
}